hi mike
this is a common issue with some windows end-users who buy p.c,s privately and from other guys,the previous owners have set specific logon details and forgot to let the new owner know the passwords ect
to disable the windows logon screen you need to gain access to user accounts in control panel however since you need to get into the windows desktop to do this you will need to use "safe mode" instead
start up your p.c and gently tap the f8 key until you see the safe mode prompt screen,then choose safe mode and press enter,you will then see a option to use system restore,click yes to continue to the safe mode desktop
then go to start>control panel>user accounts and delete any active accounts and save any changes
once all accounts have been removed restart the p.c and upon restart you will be able to load windows without any logon or passwords
also sometimes some users also set a bios password,this is done from within the bios set up and is used to create a second layer of security,however to delete this all you need to do is remove the cmos retention battery for 20 seconds and then place it back
this will reset the bios and all you need to do then is reset the time,date...reconfigure boot order..and if you wish re apply a bios password,however this isnt neesecary unless you are using your p.c on a public network or in a busy office
any problems let me know
good luck mate !