We are currently investigating an issue that Borderlands 2 appears to have with very specific processors and motherboards. Specifically, it seems to be related to AMD FX series processors and their accompanying motherboard/processor setups. Basically, there is a conflict occurring with the Steam launch due to the way these setups handle multithreading, which can cause Blue Screen errors or a system reset in some cases.
Here is a support page on the AMD website describing the issue: http://support.amd.com/us/kbarticles/Pages/STEAMGamesonAMDFXplatforms.aspx
Below is a known fix which seems to resolve most cases of AMD FX cards' compatibility issues with Steamworks titles.
Please note: This involves a BIOS update, which if done incorrectly, can cause serious permanent damage to the motherboard, so if you are not comfortable doing this yourself, please consult your system manufacturer.
1. Go to your motherboard manufacturer's website and go to their support page.
2. Find or search for your motherboard model.
3. Download the LATEST BIOS for your motherboard.
4. This will differ depending on how the BIOS is on every motherboard. Some BIOSs can update through the UEFI (Graphical BIOS) or through the use of a flash program such as AWDFLASH. Please consult your motherboard or system manual about how to update your BIOS.
5. VERY IMPORTANT. DO NOT SHUT DOWN THE PC WHILE THE BIOS IS BEING UPDATED. Doing so will "brick" the board and render it useless and inoperable.
6. Once the update is complete, your computer may or may not restart on its own. Again, read up on it in your manual or on the manufacturer's website.
7. You will need to set your BIOS back to default, and any overclock settings or boot order as well.
8. Once the system has rebooted, try launching the game again and see if the issue is resolved.
If in the event that this DOES NOT fix the issue, contact your motherboard manufacturer about the issue and they may be able to give you an updated BIOS or patch one and put it back on the support site.
Furthermore, you can also try checking for a CPU driver update. Most AMD CPUs do have a driver, so you may want to consult AMD about installing/updating one.
The following support articles may also be useful: