first thing to do: scan your laptop and the memory card with an antivirus. If its really a virus issue then deleting the virus may solve the problem.
You may put the memory card back into the original device (for ex camera or mobile phone) to see whether the files are visible there. If you can view them of the device but not on your Lappy then it can be fixed. but if its not, it might have got deleted permanently or your memory card is damaged.