hi guys i encounter a really weird prob recently

i got a new pc around April and i took a 160gb hd from my previous pc and install win 7 ultimate on it and use it on my new pc. Until now, July, one day i feel like rebooting my pc (did not reboot for like 1 month), after that my windows cannot boot at all!

I try to do system repair/recovery, but no luck. And to my surprise, i used the command prompt provided in the windows 7 dvd and browse through my C drive, i found the drive now contains the exact data BEFORE i install windows 7! Those data were from my old pc and i recognize them due to there are collections of movies on it. Anyone else encounter this before?