I'm going to try and boil down a Long and convoluted saga into a bare bones account, in the hope of getting some help.
I have an older HP Core 2 Dual-based system running WinXP with Service Pack 3.
The system came with two identical 250G SATA 2 hard drives and Vista pre-loaded.
As only one of the two physical HDs was being recognized by the system, and listed as drive "C:", I figured the other drive had died.
As I wanted to replace Vista with WinXP, I burned a "partition/erase volume" utility to a CD-ROM and used it to erase the...MBR...Master Boot Record, I think it was called...to "erase" my entire C drive. I then installed WinXP from another CD-ROM onto my C drive. So far, so good.
THEN I happened to notice (digging around in my computer case out of curiosity) that the 2nd physical HD wasn't dead...just that its power connection had come loose. (Duh!... ) So...I plugged it back in and stupidly (I guess) used the same CD-ROM utility to erase the 2nd drive's MBR(?) to "erase" that entire drive...and then the strangest thing happened: the newly "revived" and erased 2nd physical drive appeared as my C: drive...and my 1st physical drive, originally my C: drive (containing WinXP), showed up as "1". ..."1"? I've never seen a drive show up as "1"...as a number instead of a letter.
Both physical drives are connected to the proper mobo SATA "master/slave" connecters; the 1st drive as Master and the 2nd as Slave. Doesn't seem to matter. The computer won't start WinXP, since WinXP is now on drive "1" and no OS is on my "new" C: drive. In fact, after experimenting with BIOS settings, I can't even get into my BIOS screen anymore.
So...I'm going to clear the CMOS in an effort to regain BIOS access....
My questions are (1) why did the 2nd physical drive show up as "1" instead of "D"? ...And (2) is there any way to get the system to again recognize my 1st physical drive (containing my OS) as "C" instead of "1" and get the system to recognize my 2nd physical drive as "D" instead of as "C"?...short of having to erase WinXP from my 1st physical drive and reinstall it on my 2nd physical drive?