Well, you probably need to give us more details. You say "blue screen" (also known as BSOD). This implies that you can POST it (it starts but cannot load windows).
Have you tried starting in safe mode? or loading the last known good configuration? you will have to wait until the "press * to enter setup screen disappears then press F8 while it tries to start loading windows.
This will bring up a boot option menu. Try "last known good configuration" first. If that doesn't work try Safe mode.
if that doesn't work, put in the windows install disc and select "repair" current installation, it may ask if you want to do a system restore. Choose a date from before you started experiencing this problem.
Failing that you may need to re-install windows. If you do that DO NOT format the disc unless you want to lose all your data. just install over the top of the current one and your personal files should stay safe.