Puzzled by computer problem

I, for serveral months now, have had problems with my file server.

Here are the specs:
Asus P4P800SE mobo
P4 3 GIG CPU
CORSAIR CMPSU-750TX 750W PS
2 GIGS Crucial ram
DVD-ROM (hooked up to on board SATA)
OS hard drive (hooked up to on board SATA)
3 other hard drives (hooked up to SIIG SATA card)
1 DVD burner (hooked up to SIIG SATA card)

The computer will sometimes run for days with no problems but sometimes it will re-boot and I will get error messages like "fourth hard disk master error" or "NTLDR is missing". At first I thought it was the PS so I replaced it with the one mentioned above and I still have the same problem. I thought maybe the hard drive (OS) was going bad so I cloned the old one and replaced it with a new one.....I still have the same problem.

I am clueless as to what the problem could be at this point. Are there any logs in Vista that would help me identify my problem. My rig is set up to dual boot both Vista and XP and this problem still occurs regardless as to which OS I boot off of.

Before I rebuilt this thing to use as my file server it ran fine. I did not start to have problems until I installed the SIIG card so I could run all SATA dirves in my rig. The MOBO only has 2 on board SATA ports and 2 IDE ports. I did not want my rig cluttered up with any bulky IDE cables so I got the SIIG add on card so I could have all SATA drives in my rig. I suspect it could a hardware conflict with the SIIG card but I need some help as to what logs to look at in Vista, if the would even help.

Any help would be greatly appreciated.
Thanks in advance.

I tried that and I am still having trouble with it. But is has been running fine for over a week now.