PC restarts on shutdown

I've never backed up a BIOS before, so I can't really recommend anything. Any time I've done it on a Dell (the only ones I've done it on) just double clicking the downloaded bios file was all I had to do, and the computer did the rest. Looking at the Gigabyte site, it seems to be the same. The newest version is a F8 beta. Since its a beta I recommend the F7. Here is a link to the page for your product on their website:
GA-MA790XT-UD4P (rev. 1.0) - GIGABYTE - Support&Download - Motherboard - BIOS

The main thing I recommend for making sure everything goes smoothly is to try not to do it during weather conditions that can lead to a power outage and leave the computer alone while its doing its thing. Absolutely do not touch any buttons or touch the power cord unless asked to by a prompt on the screen.

It depends on the computer. I think my dads took around 20 minutes, but its been a year since I did it. A lot of places I look at say 2-10 minutes, depending on the bios chip and other hardware. Do you have another computer you can use in the rare case something goes wrong? Do you have a USB you can back the file up on?

Just copy it to the flash drive. The old laptop could be useful in a worst case scenario. I think you should go ahead a do the bios update. Let it run like it needs to and absolutely don't interrupt it unless someone advises you to.

Maybe we are misunderstanding each other. Go to the site I linked to earlier. Download the F7 or F8 and make a copy of that .exe on to your flash drive just so you have it in case something goes wrong. There are ways to redo the bios update from a flash drive. I don't think you'll need it, but I want to air on the side of caution since you feel a little uncomfortable with it. You shouldn't need to back up the current one if you have told me the right motherboard. A back-up of the current bios is only used when a person is unsure of what mobo they have.

That is my understanding, based on what I have read. Since you are getting a full .exe you should be able to do it that way. I just checked and it looks like you need to format the flash drive as FAT or FAT32. Format it if necessary.