low on ram makes some good points. however he or she made a few errors.
firstly spybot though freeware in my experiance caused more trouble than it fixed.
adaware is made by and supplied by lavasoft a sweedish company. there is a free version and a licened paid version.
I've heard bad things about AVG (like it has caused more problems than it prevented.
msconfig is part of the windows XP operating system.
all you need to do is click, start. run and type in the ltext box msconfig and the program should start. though you need to be able to boot to your operating systerm first.
as you are obviousley a relative novice to intermediate user, the advance utilities are not advised in your case as you could end up causing your system to become 100% unusable.
in your case the problem could be one where your hard drive may be failing or the powersupply unit may be failing or failed on the rail supplying your hard drive.
first open up your computer case and attempt to swap around the powersupply cables.
if no spare cables do a simple swap Hard Drive to CD/DVD drive.
now try to power up the computer, if it starts normally then your power supply may be failing and so you should attempt to get a replacement as soon as you can.
if swapping the cables fails to solve the problem then recheck the cables. push the data cable in properly to the main board and to your hard drive and CD/DVD, double check the power cables are seated correctly (firmly pushed into the connectors on the drives.
if your drive is connected properly and booting up slowly, then it could be that your system has a hard drive that is badly fragmented so you may like to run defrag to fix the problem.
you should run a disc check too as well as a full virus scan.
if your computer boots normally (but slowly) go to http://housecall.trendmicro.com allow the scan to run make sure you select scan everything. also make sure to set to clean what it can and delete the uncleanable. (or quarantine if you want to risk the quarantined items will be cleaned in future updates and scans.
once the malware scan is complete, run a disc check then defrag.
all the above assuming that your computer will boot to your operating system so you can sign in as administrator to take the required steps to fix your computer.
if the hard drive will not boot or is not found then it is as said above a duff connection or a dead drive or power supply.
check on powering up the computer that your hard drive shows correctly.
you should not need to go to the computer bios to solve this problem, but if you have added other software or hardware then you may need to go to the bios and reset it.
getting in to the bios varies from computer to computer (it depends on the chipset on the system board) you will see during boot (for a second or less how to get in to the bios/cmos) note it and after the bios finds your drives and before it starts to boot from your operating system use the noted command key(s) to get to the bios.
now depending on your configuration and chipset you may need to go through all the menu options until you find the options that you need, namely to check that the computer is set to boot from your hard drive. if more than one hard drive make sure the correct drive is configured as the first boot drive.
you may also need to find the settings to reset the bios.
it all depends on system configuration. as i said.
if your hard drive is failing and that is the reason it is slow you may like to consider buying a new hard drive or two. install one drive as a back up/ second drive in the system. use back up software to make a backup of your failing hard drive.
next remove the old hard drive and install the second new hard drive.
reinstall the windows operating system and then re-run the backup program to restore your computer to as it was before. though if using XP you will need to re-register. easy to do don't worry about it.
power supply and two 250GB hard drives can be yours for around £120 or less delivered in the UK from dabs.com.
good luck. on trouble shooting this error!
before all of the above attempt to boot from the operating system CD and select restore mode. when asked for which os to repair press 1 (only one operating system is installed)
you will now be asked for the admin password (xp service pack two oem CD) press enter (no password)
type chkdsk /? for a list of options and details of how to use the command. make sure to run scan and fix to repair any problems. your computer may need to be restarted for the scan to start. this is normal. though depending on the size of the drive it could take a while to scan and fix!
remember to check what programs you have selected to start when your computer starts, and remove all items listed in the start up folder in the programs area of windows start menu (if that makes any sense to you).
I appologise here for this seemingly longwinded response but your question was limited to say the least, so i have attempted to cover most if not all eventualaties and what you need to do. if you are not confident about any of the tasks detailed above get professional help to either walk you through step by step or have them do the work for you. though if your system is old this could cost you more than the system is worth to fix.
one last point, if you are using a shop bought computer chances are you have a non seagate hard drive installed. if your drive is not a seagate you can pretty much guarantee your drive is failing and needs to be replaced within a week or two at the most. however a seagate drive reporting the same problems can be recovered easily from such an error many times before it actually dies completely.
also remember this could be a form of malwware causing the erro so make sure the malware scan is completed at the first opertunity!
on the point of the software listed, always go to the publisher of the software when ever possible as failing to do so could result in you getting tampered with software that could conatin all kinds of malware. (i've been there and done that, that is how i know).
also if you have a peer to peer file share service installed on your computer this can slow down your computer as your network connections are re-connected before you can actually log in on a windows xp based system espescially true when connecting via LAN to other computers or a broadband internet connection.