How to fix a “stop:0x0000007b inaccessible boot device”

i have a dell optiplex GX260 with a windows 2000, Just yesterday i was transfering some data from my pc to a thumb drive when the Pc froze. Pressing the alt+ctrl didnt help so my sis had the pc shut down by holding down the start button for a few mins, i then start it up again but this time windows couldnt complete running, it would only load halfway and the stop:0x0000007b inaccessible bott device came up. i have tried starting in up on safe mode but the same blue screen comes up b4 windows could completely load. i have even tried downloading a boot check disk and booting up from there but it would just say “invaild disk”
i dont know what else to do, pls help.