PC won't boot up

I have a Compaq Presario SR1000 which was working fine a couple of days ago. The monitor on my 2nd PC died so I borrowed the one from the Compaq. Having got a replacement monitor today I put the old monitor back on the Compaq and started it up. I get the Compaq logo, it starts to boot and I get a screen saying "Windows didn't start properly etc" and gives me the options of Safe Mode, CP with CD-Rom support, CP with Networking, Last Known Good Config and Normal.
None of them work, it simply keeps endlessly going round this loop.
I have a Win XP CD which I have tried inserting and getting it to boot only from the CD-ROM and still nothing.
Does anyone have any idea before I resort to tool No1??????
Incidentally, I also have exactly the same issue on an old Compaq Armada E500 laptop !!
Thanks