If this PC is less than a year old, use the free included tech support to resolve failure to enter BIOS setup. It may need to be RMA'd.
If not again try entering BIOS setup to reset BIOS to optimal defaults. If it fails again, try resetting the CMOS using the battery jumper method here: Clear CMOS - 3 Ways to Clear the CMOS - Reset BIOS
Look on the Support Downloads webpage for the computer or mobo model to see if a newer BIOS update exists and if it can be flashed from boot. Follow steps in the ReadME file precisely or you could brick your mobo.
Try also booting the Windows 7 DVD Repair console or Repair CD using the one-time BIOS Boot menu key to run Startup Repair.
If you don't have DVD make a Repair CD from a Windows 7 computer with the same bit-version: System Repair Disc - Create