dimension e520 Win7x64 flashing underscore after bios update

hello, i have this problem.

I installed windows 7 home premius 64 bit after buying this computer used off craigslist. everything worked fine until last night when I decided to update the bios. the update was successful, but now the computer is having trouble recognising the hard drive, which is I believe the stock 25 GB sata drive. when i do get it set to detect properly, all that happens after POST is a flashing underscore in the top left of the screen. I usedd the f12 boot menu to run a s.m.a.r.t. check and the drive came back as healthy. i also do not have a second tower to pop it into and check. does anyone know what the problem could be?