Computer wont start up fully
Your boot menu for Windows is corrupt. Try to boot from the windows installation disc and make sure to key any key when told to boot off the disc. Once the windows files load, you will have a choice of what to do next. If you have XP, choose the repair option and you will be faced with a black DOS screen...after the blinking cursor type
FIXBOOT hit enter
Try to boot the computer without the disc in it. If it does not boot, then boot off disc again and this time type:
FIXMBR hit yes and enter
Try once again to boot without the disc.
Also try to boot into safe mode by tapping F8 when you see the Compaq name come up during starting. If you can get to the multiple boot up option screen, scroll to "Safe mode with networking" and choose that. If it boots then you can go to the start button > accessories > system tools > system restore > choose a restore point back a day or two and follow the prompts.
If you have Vista, boot off the disc and choose start up repair. If that doesn't work, boot again and choose restore computer to an earlier time. Again choose a restore point back a few days. Good luck ParrotHead PC Repair