No Operating System Found

I am working on a HP PC with an ME OS
900 Mghz AMD Duron
40 Gb HD (1 Gb used)
128 Mb Ram

Here's the problem....
When I got this thing they couldnt even boot up
It would get to the ME screen and shut down

I went in via safe mode (wanted to go in via c: and do a scandisk first but would not give me any options other than safe mode) went back to a restore point 2 months ago, and then began Uninstalling the MYRIAD of games her kid downloaded.

There were at least 40 that I uninstalled and a few other programs that were adware (search bars - several - for their browser)

Everything was going swimingly until I decided to try to install my Thumb drives that house all of my little utilities, and then it started.... on every boot up..... NO OPERATING SYSTEM FOUND. The USB ports were not recognizing the Thumb Drives so I installed the software.... then the problem began......

The only way I can get in now is to rapidly and repeatedly hit F10 and it goes right into (after about a 2 minute pause) ME.

Then ran Ad-Aware and Spybot and got rid of 460 items (most I've seen yet).
Each time I did anything I always rebooted.
Ran her McAfee and no virus.

Ran a complete Scandisk and Defrag also (during defrag I got a message that I needed to Scandisk again - said no and continued with the defrag)

Now it's running quickly (unlike before) but I still can not get in without the rapid hitting of the F10 key.

Does anyone have any suggestions (short of reformatting the HD - that's the last resort).

Flummuxed In Florida
Linda