6GB Fat partition?

mouse stuttered for a few seconds, then a lock-up.
Reboot and got invalid system disk etc.
Recovery software could not identify anything.
Fdisk/mbr, booted ok but 2 partitions missing.(was 3 partitions with the first being 2GB fat others fat or fat 32)
Recovery software now reports 1 unknown partition and partition magic reports a single 5.9 Gig fat partition.
Smells like a virus but virus scan shows drive clean.
Any advice appreciated