Drive A Error system halt

[patio]

Best way is to borrow a known good PSU of the same wattage or greater amd swap it in there...you'll know overnite if it's the culprit.

[crotchetybob]

Motherboard documentation can be found http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01635688&tmp_task=prodinfoCategory&lc=en&dlc=en&cc=us&site=null&key=null&product=3867529#N31 although I dont see where it specifies the type of ROM.  I went ahead and tried to reset the bios password, in what ended as a futile attempt.

EDIT-Although, it does have "One SPI (ROM programming) connector " Is this helpful at all?

[Computer_Commando]

Did you clear the CMOS settings according to the instructions given in the link you provided?

[crotchetybob]

Yes.  Switched pins for 5-10 secs, then switched back. No results.

[Geek-9pm]

The manual says there are two resets. One for CMOS, the other for password.

Also, the HP web site indicates that what they call ROM is, if fact, programmable. There is a method to reprogram the "ROM" which may fix the check sum error and all other issues. The OP could contact HP and they can tell you where the details are found. The OP needs a good working floppy drive to re program the BIOS OM.

EDITS:
Same issue
http://h30434.www3.hp.com/t5/Desktop-Hardware/BIOS-ROM-Checksum-error/td-p/60306
BIOS for MS-7548 motherboard
http://h10025.www1.hp.com/ewfrf/wc/softwareDownloadIndex?cc=us&lc=en&dlc=en&softwareitem=pv-73188-1
I am not sure if that will work. My HP is not the same .
But the link above is for the board  the OP says he has.

[Salmon Trout]

Could you please give the model number of the PC or motherboard.

He already did

my motherboard (MS-7548).

[Geek-9pm]

Sparse information from HP indicates that the
"ROM checksum error"
is not the same as the
CMOS checksum error.

To fix that "ROM checksum error"m one can:
1. Replace the motherboard.
2. Try to boot a floppy with the ROM recovery program
3. Some other repair or  recovery method not well documented.*

I did not find the exact information on the HP site. Other sources say that the "ROM checksum error" waits for the floppy drive. The floppy is to have the recovery program for that BIOS chip.
I had an I Intel motherboard a few years ago with that feature. But I don't know if the OP 'motherboard has that feature. It is not something you often run into.

* There is a gizmo to program the BIOS with no power to the motherboard. Without removing the chip.