non system disk will not allow you to boot to windows... hes stuck at the bios screen and bios is looking for a hard drive to boot to.
Yes it can be a flash drive, remove it... ( unplug all usb devices except mouse and keyboard ) try to reboot. If you continue to get non system disk chances are you have a hard drive thats failed or a motherboard controller thats failed. You could also have accidentally deleted ( or a virus deleted ) the windows boot partition.
Regardless of which item is causing the issue... ultimately bios is looking for a boot partition ( os ) to start up. It cant find one.

If you have another computer you could download and create a bootable cd from Hirens boot disk or .. a falcon 4 boot disk and use mini xp environment. Once you get a hirens / xp mini os booted and running you can use one of the hard drive testing tools on the disk to scan and verify the disk.

I hope that helps..

:)