on boot up press the bios setup key, f10 in compaqs case, there should be a section for optimum settings, set as minimum settings and reboot then goto boot up and press f5 or f8 to force into safe mode, try safe mode with command prompt , and run chkdsk, just type it in press enter, then once thats completed reboot the unit again and try the f5 f8 and boot into safe mode windows, see if that will boot if that goes in, then restart the system again, that should have reset the whole registry startup
ianc, November 2008