When you restart does your computer keep showing the blue screen?
Have you changed any hardware recently (even something as simple as plugging in a new mouse, graphics card, external hard drive or USB flash drive etc.)
Usually the blue screen indicates there is a major problem with a new piece of hardware that's causing a fatal error, causing Windows to crash.
The first thing is to try and enter safe mode. To do this, turn on your computer and as it is booting repeatedly press the F8 key (not too fast, but not too slow either, just repeatedly press it).
If you are given the option to start in safe mode, select that option and try starting your computer. If it seems to work, try using safe mode to back-up all your files in case anything goes wrong.
Now look in your start menu all programs list for a 'System Recovery' utility or something of the sorts (this will vary based on your manufacturer). If you find it, try running the recover utility and see if it can restore Windows to manufacturer's defaults.
If not, try rebooting your computer and look for something like
"Press F11 to start recovery" and push the appropriate key and follow the wizard.
If still no luck, it's best to contact the manufacturer so they can ship out the recovery discs to you (if you really push, they usually do this for free - at least the first time).