Black screen, white flashing underscore, BIOS Skip?


Sep 2, 2011
This all started last night. I have no idea who the culprit for this despicable matter is. Actually it's not that bad, just a little annoying.

I decided to restart my computer after doing a Windows Update, all was good, went on my iPod touch while it was rebooting then I noticed a black screen with a white flashing underscore. I immediately freaked out, try hitting enter, CTRL, ALT, Del. Nothing so I hit the reboot button on my computer. Windows loaded normally... After this happening I became concerned... I immediately googled it, and asked other websites, and got a lot of "it's your boot order, make your HDD the primary device." no it was not my boot order... I then did a memory test, and did the restart now option, the computer restarted, Skipped the BIOS and went to the black screen with flashing underscore... I hit the reboot button and it went to the memory test and everything checked out... Even more concerned I did a Hard Drive check. After about two hours of that it went to the black screen with the underscore... At this point I said forget it, I'm going to bed...

This morning before work, I checked to see if it was the HDD or GPU... Unplugged the HDD, black screen, white underscore... Unplugged the GPU... Black Screen, white underscore... Went to work... Came home, checked if there was a disc in the drive, there wasn't so I googled some more, found something about unplugging the power cord, instead I plugged in a different one and it booted up fine. After a few hours of running I decided to reboot, black screen with white underscore.... So I rebooted with the button on my case again and it booted normally...

After all that I tried to do a System Repair, it wouldn't allow me because of USB devices being plugged in? I unplugged everything but the mouse and it still wouldn't let me...

So I did a FixMbr and haven't rebooted since... I'm scared that if I do I will get a long lasting black screen/white underscore again....

What could this mean?!?!

Edit: I forgot to mention that I built the PC in the first week of August, and installed a Video Card and a couple fans last week or two.


AMD Phenom II X4 955 Black Edition

ASUS M4A88TD-M/USB3 Motherboard

Samsung Spinpoint F3 1 TB

G.Skill Ripjaws 1333 (2x4GB)

Antec Earthwatts Green Edition 650 PSU

XFX Radeon 6870 Standard Edition

Windows 7 Professional 64 bit.


Apr 24, 2011
Well, looking at this logically - all your problems appear to be stemming from either your BIOS - or your motherboard. Essentially there is a problem in boot up. Am assuming that when it goes to windows all is hunky dory? That underscore does indicate a boot priority mixup. I have the same darn indicator despite my boot up being setup properly too - I also can't access the BIOS. Maybe it's ASUS mobos.

Essentially - by removing computer parts from this messy equation - and coming by the same problem - you have narrowed down the field of potential failures. It is unlikely that by unplugging the HDD and having the same thing happen that the problem has anything to do with the HDD. So let's forget about that and forget doing Fixmbr.

I'd also forget about checking your ram. If your memory was a problem - you'd get an error message or you wouldn't get anything at all cos a computer without memory isn't a computer. Same with the video card/onboard video - its job is to display and it appears to be doing that. I'm not saying weird stuff don't happen - it's just extremely unlikely.

Right, you said you removed the HDD - did you also disconnect the CD-ROM? What we're looking for is a message asking for a boot device. If you don't have any boot devices plugged in - and it still goes to that black screen, white underscore - then there is a definite problem with either the BIOS, BIOS chip, or your motherboard. Best bet is get the whole thing replaced. If it asks for a bootup device - and does so consistently - we can start narrowing down problems even more, but possibly in a different direction.

You mentioned that at times the process skips the BIOS - what do you mean? That you can't access the BIOS or it goes straight to the underscore?
Can you access the BIOS at all + make changes and save them?

Here are a few things you could try, they're not necessarily fixes we just need to see what happens:

If you can get a copy of your BIOS from the manufacturer's website - you could try overwriting your existing BIOS. It is possible for your BIOS to be infected, possibly through a virus from your HDD.

Clear the BIOS memory. There is a little battery on your motherboard - take it out - wait for 20 seconds - then put it back in. This should force your computer to allow you to access the BIOS if you're unable to otherwise. What you want to check when you're in the BIOS - is that if you're making changes that they are being saved. If your BIOS isn't saving changes - you could replace the battery for the motherboard. Quite often the ones supplied are crap - and will need replaced anyway - but it is also possible that a duff battery is causing the BIOS to stay at defaults.

Do you have any spare parts? Can you put your HDD, GPU in another computer? As I said - I really don't think these could be the problem from what you're saying, but when dealing with this kind of thing - I've found that you need your head cleared of possibilities to find the answer. Check the parts out if you can and see if a perfectly good computer encounters the same problem. Don't be worried about that machine having the BIOS screwed up - all potential viruses that infect the BIOS is BIOS and motherboard specific. Which would be a shame if the other computer has the same BIOS and motherboard. :)

Ok, try these things and come back if you have anything new.


Sep 2, 2011
I'll try all those things if the problem persists again however...

Ever since the "fixmbr" it hasn't been an issue...

It's been a good two days now I believe and have not seen a black screen with white underscore.

Thanks for the reply though!