boot drive loses C letter

[Vlad]

I had 3 HDD in my PC.The first 160G(with 20 g bootable
partition) was on Promise ATA controller,2 others 40G were
on primary IDE,CD on second IDE,External SCSI HP CDRW,and
160G on external USB.Everything worked fine until i decide
to switch from SCSI CDRW to IDE.
I uninstall SCSI controller from system,shut it down,
remove it,put IDE,turned on.And all the sadden one of my
40g became C drive.
From now on,i cant install any HDD in order for me to boot
properly.I played with controllers,Masters,Slaves
etc.Reinstall WINXP.
BIOS shows all HDD in proper order,but after every attempt
to put second HDD,i have to boot from WINXP CD ang rebuild
bootcfg.
On the top of it(not sure it's related)USB HDD went down
with no reason.
I've spent 24 hrs already.No sure where to go anymore.

 

[Pavel]

What is unclear is that I do not understand how you determine that this 40g
drive is now C? Is there OS on this drive? Is the drive formatted as fat32
and you get DOS prompt? At any point does WindowsXP try to load?

 

[Guest]

I boot from ERD commander,so i can see it.There's no OS
neither on that HD nor any other i'm trying to add besides
the main one.