Help! 'Invalid partition table_',then cant access advancd boot options

I got the blue screen of death and it restarted...

It read 'Invalid partition table_'

Since then i have tried to press f5 and f8 to access the advanced boot but nothing comes up.

I have also been into bios to try and see what harddrive is assigned to boot from and all okay.

I dont have a disk drive on this computer as its a custom build but i installed windows 7 originally using a usb pen and set the boot to boot from that and installed it. Even tried sticking the usb stick with the setup again and it wont seem to reboot from that eith.

Any help would be much apreciated thanks in advance

Reset the BIOS to defaults taking note first of any UEFI, CSM, and the SATA controller setting (should be AHCI). Set the Hard drive first to boot in BIOS boot priority. Is the HD listed?

Your USB stick should then boot off the one-time BIOS Boot menu key. Check under USB, Removable or HD's and you may need to expand a listing with a +.

If the stick won't boot then try unplugging the HD and all other peripherals. If the HD is blocking stick's boot then it has boot sector corruption, may need to be slaved to another PC to try to rescue its data and then wipe it for reinstall in the original PC.

Next test stick in another PC to see if its lost bootability. If so make another from Troubleshooting Windows 7 Failure to Start then work through those steps to try to repair and restart Win7, leading up to if necessary rescuiing your files to do the superior Clean Reinstall - Factory OEM Windows 7.

If you'll report back as you go there may be other repairs indicated.