Corrupt or Missing BIOS - no POST, can't boot from USB or CD

Dell Optiplex 790 (SFF). Will not boot - Diagnostics are Amber Power light (steady) and diagnostic lights 2,3 & 4 flashing amber - this indicates a corrupt or missing BIOS. Turning on, the PC powers up but immediately starts the flashing diagnostic lights. This is my daughters computer and appears to have just randomly happened.

Had the issue confirmed by Dell, but as I bought it second hand and have no idea which company originally owned it, I cant get a repair via any warranty.

Have downloaded the BIOS from Dell and created an MS-Dos start-up disk (via Rufus) on both a USB drive and a CD. The PC will not attempt to boot from either source and continues to flash the diagnostic lights. As I have no access, I cant change the boot sequence.

Is there any method to force a boot from either USB or CD? - or an alternate option?

Most forums tend to recommend a new motherboard when this happens in Dells, but be great to avoid this if possible.

Hey, sorry to hear

Did you try clearing the CMOS? you may need to search how to clear it for your PC

Also do you get any action on the screen when you power up? You can try Boot Menu option (usually lists the key to press when BIOS first screen) which is a one time "boot from" menu.

After posting I followed a thread on clearing the CMOS. Bit tight inside the case, so the best option was to remove and re-seat the battery, which I did. Made no difference.

The screen remains blank throughout. Tried the function keys on start-up to try and access the bios, but no joy.

If I have to replace the motherboard, is the dell board a standard sized micro board? (might be a cheaper and easier option to replace with something other than Dell).

Danter, did you solve this issue? If so, what did you do?

I have an Optiplex 990 SFF giving the same diagnostic code.

Thanks!

In the end I replaced the motherboard and all is now working as it should.
Expensive to purchase in Australia (where I am) but found a cheap second hand board from the US for about $30 from memory. Easy install and rebooted without a hiccup.

Besides the wait for the board, it was an easier option than the hours wasted attempting to find a solution that I suspect was never going to work.

Danter,

Thanks for the response. I called Dell's out of warranty hardware repair number and the service rep (from India) indicated the MOBO was this issue and they could send someone to fix it for US$319. Based on that, I ordered a "New" MOBO from eBay for US$37 including shipping. It's good knowing a MOBO swap fixed your issue - my next candidate, the CPU, is a lot more $$$.

If the BIOS flash is in a socket (which seems unlikely) I'll try swapping it.

The MOBO will be here in a week. I'll report back as to the level of my success then.

Thanks guys.

tjf

I swapped out my Optiplex 990 SFF motherboard which solved my issue. The computer runs again!

The only socket part on the 990 SFF motherboard is the CPU so swapping the chip containing the BIOS isn't practical - especially given a new motherboard costs US$37!

Thanks everyone for the help!!!

tjf