If you have a 2 TB consisting of 4 500GB drives in a RAID 0 and one fails, then you have lost your data. There is no fault tolerance in RAID 0. You could use a company like OnTrack.
In your case, it is better to consult your problem to the nearest computer store or a computer hardware expert in your area. This is because your computer system needs to be carefully checked especially on its hardware parts and configurations.