Someone was on my pc last night, and they were TRYING to change my SID for some reason.

I closed the SID changing program before it finished doing whatever it was doing, then did a system RESTORE, because when I restarted my pc, it was all wonky.

When I booted my system again, after it loaded windows, it came to a blank screen with my mouse cursor, where it was supposed to be the log-in screen.

I've tried safe-mode, but it only has the same results. It won't boot from a disk either, and it won't run system checks.

My OS is Win7 home premium.

Can anyone help me, or is my system shot?

And please, no "your problem is you don't have linux/osx" jokes.Who has access to this PC ? ?
Why would they be attempting ( which isn't easy ) to change your SID for NEFARIOUS reasons ? ?

This really needs more info than what's been given...help us to help you.Reference.
In Windows, what is the SID (security identifier)?Thanks for your help guys, but I solved the problem by just reinstalling windows on my system.

THANKFULLY, Windows saves all of my old files in a "windows.old" folder on my hard-drive. (: