Try starting in safe mode (hit F8 during startup, after the BIOS checks).
That loads a default driver that should work any monitor. If the PC boots,
then you are likely correct that the problem is the video driver. In that
case, download the latest, hopefully best, driver from the video card maker.
If the PC has no video card, then look to the PC maker's support site for a
driver for the on-board (on motherboard) video. Install the driver from
within safe mode, then reboot and go into full windows mode. Since you
mention that the PC is a COMPAQ, I would start with their support site.
Check FAQs, drivers, search on problems with video and/or rebooting, etc.
They are likely to have some instructions on installing/re-installing video
drivers. And, you can always send them an email.
You might also need a driver for the monitor, separate from the video card
driver. However, monitor drivers are normally not required for anything but
special options. But, if the monitor is somehow "unique", then it might
need a driver for XP, beyond any default drivers XP already has. Again, if
the monitor came from COMPAQ, see them for drivers.
If you can get the PC working somewhat, try Windows Update. That can
sometiumes find a new/improved driver for hardware.
If you can get the PC working, even in safe mode, try running a disk check
to be sure that you have no problems with the file system. Open a command
prompt and type CHKDSK C: /R say yes when it asks about doing this
during the next boot, then reboot the PC. The "/R" option can take a long
time to run, but it tries to check/fix a lot of file-related problems.
BUT, if you suspect hardware problems, instead of driver problems, try
booting the PC from a rescue CD. You may need to change the BIOS settings
to boot from CD before interal hard drive. See COMPAQ documentation for
detailed information on how to do that. Try one of the following:
http://ubcd.sourceforge.net/ many testing tools...just avoid options like
"format", "erase", "wipe", "partition", etc !
http://www.knopper.net/knoppix/index-en.html full LINUX operating system
and applicaitons suite...will not install on hard drive
If either of these boots the PC, then it is likely the problem within XP is
software related. But, if the PC can not be booted by one of these, then
you may need to worry about more than just drivers.