bios or mobo?

Wrong bootdisk (for much older system) was inserted in floppy drive of HP pavilion and booted. Since then only startup screen loads and then tries to boot, refuses to acknowledge the harddrive and starts to access A:,and gives a black screen with upperlefthand cursor.I am able to enter BIOS Ran diag. on sys., harddrive, in dos.
Everything ok. Transplanted harddrive to other comp. Fine. reformatted, fresh os install. Still nothing. I accessed BIOS and restored default settings. Didn't help.Reset cmos. Correctly reflashed BIOS. Did't help.Is it possible to have a bad BIOS chip that seems to function correctly.Running out of options. Any ideas. Any comments would be greatly appreciated.

What options in BIOS does it give you for the HD? does it Auto Detect or do you have to manully set it?

IF the drive works in another machine leeds me to think the HD is fine.
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Could always try doing an fdisk /mbr from c:/> prompt. Am not sure if this would work since HDD is ok in another machine, but it takes 2 seconds and can only make things better...

Other than that, perhaps try plugging HDD IDE cable into the other port on the mobo.

Very strange that the prob happened after using old boot disk.... Wierd. But like Anna says, maybe it is a problem with the BIOS settings... If BIOS cannot auto-detect, make a note of the info on HD and add it manuly as a user defined HDD...

Make sure you have no viruses floating around... Just my 2c worth.

Thanks for the replys. Considered and tried them all. I was just about to give up. On a whim I tried installing WinME.So far I had only tried win98 restore cd. Strange but true after installing and rebooting the computer it ran like a charm. Maybe it was missing a driver and winme has a larger driver bundle. Or that it searched in more detail for missing PNP components. Got me. The main thing is it works. Again thanks for the tips.