Hdd detected in bios, can't boot however

[Jaket1000]

I have an upgrade Dell Optiplex 755 and all the sudden my hard drive is not being bootable. It is detected in the bios but I can't boot from it at all, unfortantly I can't test on another pc

 

[popatim]

Boot from a windows install media (DVD, Flashdrive) and run startup repair a few times to see if that will resolve the boot problem.
I'm assuming you've made no changes in the system and that all the installed drives are being detected normally.