Thanks guys! I didn't call Microsoft (mostly because I couldn't find a support number anywhere on their website and, inserting the product ID of my operating system, their website told me no free support would be available and sending a lowly email would've cost me >70 euros). I had already run a memory test before I flashed the BIOS, and reinstalled Windows. You're absolutely right, it's working fine now.
Thanks a lot for the help!!