Hi, people I can really need your help on this one!!

due to some misterious crash on our comp, it doesnt seem to have a C-drive anymore. I think that because of some virus a antivirussystem deleted a certain file. everytime when I restarted the comp to format, more memory dissapeared.
I wasn't able to format my comp.
only and old dos system managed to created a partition of 2000Mb
of the old 10000Mb
in bios and fdisk they recognize the size of the harddrive, I cant see how to create a bigger partion then 2000Mb
when I try to format the C-drive it only formats the 2000Mb
when running a diagnostic program
alarms popup with things like: wrong number of clusters, invalid FAT type etc..

can somebody plzzzz help me with this 'cause I haven't enough money for another comp...