My 'system' has for the third time gone critical!!

However unlike the other times, when I have rebuilt the offending drive, this time the drive has gone 'off line'. I'm a complete novice, (I did not install setup and can't contact the man who did) so please keep it simple!

Other than knowing I have four 2TB WDC drives paired on ports 1 & 4 and ports 2 & 3, I know little else!!

The drive in port 3 states its 'offline' and does not appear in logical drives, just the one drive in port 2

Running Windows 8. with Stardock to make it look like Windows 7

Anyone know what to do other than buy and replace the drive?