Updating bios compaq evo
If you cannot get into Safe Mode then you can also try booting to run a full scan with one of the FREE Bootable Anti Virus Rescue CDs - Download List .
If you need a Win7 disk to boot you can burn a System Repair Disk on another Win7 PC as long as it has the same 32- or 64-bit version, use an enhanced Repair disk available for download at Easy Recovery Essentials, or refer to Step 1 in Clean Reinstall Windows 7 for installation media which contains repair System Recovery Options or if necessary can be used for reinstall.
This is a quick operation that is often useful when non-booting is due to a recent system change. Boot into System Recovery Options via the F8 Advanced Boot Options menu or disk as shown in blue link tutorial, open a Command Line to run a full Disk Check (chkdsk /f) on both the System partition and Windows partition (if they're not one and the same).
On a Legacy install to MBR disk, confirm the Partition Marked Active is the 100mb System Reserved (preferred if you have it) or Windows 7 partition (if you don't), run Startup Repair repeatedly up to 3 separate times with reboots in between each - no matter what it reports.
At this point the assistance of the System Security forum can be requested to provide guidance on a diagnostic tool to run a scan in the RE(covery) environment.
Scan results will determine the next course of action.
A UEFI install has a EFI System partition instead of System Reserved, and a (hidden) MSR partition, can only boot from a GPT disk.