SO I went to turn on my computer the other day and it started the boot process but it now hangs on the BIOS check SCREEN when it's detecting hard drives.

I thought maybe it was just a software issue, so I tried to reinstall windows from a cd, but it couldn't find the SATA HD. From there I thought maybe the HD went bad, so I tried an old backup IDE HD I had. I was able to install windows xp on this and boot up successfully. So I bought a new SATA HD and installed Vista on it and it went fine.

But I decided that I remembered why I didn't like Vista, so I tried to install XP on it instead. XP starts to install just fine, but when it reboots to continue the install, once it gets to the HD, the screen shows random characters and the old "missing NTLDR" message pops up.

I am at a loss for what the actual problem is. It could be software or hardware, but I've tried just about everything I can think of:

- reinstalled OS's
- switched HDs
- switched motherboards
- switched RAM
- reset CMOS battery
- changed SATA cables

Basically, it just seems like it hates anything that deals with a SATA HD and that the problem lies there. But why did it let me install Vista on the SATA HD but XP screwed up? It's like for every thing that seems logical there is ANOTHER point that CONTRADICTS it. I should also add that overheating has never been an issue and doesn't seem to be the problem here.

Here's my system:

ASUS P5N-EM motherboard
Intel Core2 Quad CPU 2.40 GHz
4 GB RAM
Western Digital 1 TB HD
Using on-board graphics and SOUND on motherboard

I've built and fixed my own systems for years and this one has me completely stumped. Please help if you can!
Just guessing:
drive not formatted or set to active.
or from my experience, if Vista is still loaded, it will not allow an older operating system to replace it.
Is Vista deleted from the drive?I had a similar problem on a different P5n SERIES board. If you happen to have anything attached to the IDE/PATA connectors (HDDs, CDs) the SATA driver freaks out. If that's the case, unplug all the IDE/PATA cables and the install should go smoothly and afterward, all the drives will get along. Otherwise, I wish you luck.