This may be a lengthy explanation so I apologize in advance. I have a user that previously had a Seagate SATA drive with Windows Vista pre-installed in a Dell machine. When I got the computer, I was unable to boot Windows, get into Safe Mode with or without command prompt, use a last known configuration, or use the provided Windows Vista CD from Dell. I will add that when trying to boot Windows normally from the boot menu, I would get a BSOD with a "Unmountable_Boot_Volume" error.
I was able to run a diagnostic on the drive that came back with no errors so I assumed a MBR or some type of boot sector issue. I took this drive out and threw in a brand new similar Seagate SATA drive. I went through a brand new Windows Vista installation on the new drive and booted up just fine with no problems. Once I ran through the updates and made sure the rest of the system was working correctly, I added the old drive in as well to see the results and possibly run a drive repair. Once I turned on the Sata-3 port in BIOS for the motherboard to see the new drive, the new Windows Vista install stopped booting correctly. I was able to load into Windows but as soon as the OS began to load, Explorer would crash forcing me to shut down.
With both drives installed, I am unable to boot into safe mode as it freezes during the loading process. I was, however, able to get to Safe Mode with Command Prompt at one point. From command prompt, I was unable to view any contents of the old drive. All I could view was apparently the recovery partition that Dell had pre-installed but I was able to correctly view every directory of the new drive. BIOS appears to automatically set these 2 drives up in a Raid config and everything is detecting correctly in BIOS when both drives are installed.
Now I know that Windows Vista can have problems with dual boot scenarios but this is a first time that I have ran into this type of issue with Vista. I assumed that once I installed the new drive with a fresh install, that I should be able to boot from that allowing me to fully repair and backup the old drive. However, it appears that once the new drive boots, somehow the previous install on the old drive is conflicting.
Thanks for the replies Emerald. I was able to remedy the situation all the same.
What I had to do was use another system with a Windows Vista install. I plugged my customers drive in and booted up without any issues. I've been able to back the drive up and am currently in the process of formatting it so I can give it back to him to use as a backup drive. Now, obviously, this didnt answer my initial problem but its a solution at least.
If anyone happens to come across this issue, my only recommendation would be to check that motherboard drivers are updated, BIOS settings are correct with relation to boot orders and RAID configs, and possibly same with BIOS updates. This is just a guess as the drive worked correctly as a secondary with the only difference being a different motherboard/BIOS.