Can you do a system restore to when it was working properly?
(Maybe not if you can't get Windows to load at all.)
If it is a laptop, unplug, remove the battery, wait a minute, reinstall the battery and reboot.
If you are able to exit when the error message appears, try rebooting in safe mode.
If all else fails, you can reinstall 7.
Would also try googling the error message and going through the various related threads until you stumble on to a fix that works.
Maybe HP tech support?