My computer is screwed, please HELP.

[ferrari550]

Hey guys, i am in desperate need of answers. My computer is messed up, when i turn it on i cannot open anything. a couple of days ago a warning came up and said my computer was at risk but it did not give me a chance to fix it. so now nothing will open, the start button in the corner will not work anymore. so all i can is click items on the desktop, but they will not open. nothing will open. anyone ever heard of anything like this??

i am on my roommates computer to write this, so if anyone has any idea what to do or what i can do please let me know. i know reformating is an option but i do not want to lose my 40gigs in car videos, they are videos of things from years ago that i do not want to lose.

Thanks guys