RAID Problem Please Help

Hey everyone,
I recently built a computer, on which I created a RAID 10. My computer consists of an ASUS P6T Deluxe V2 Motherboard and four WD RE3 750gb hard drives. I installed my operating system on the RAID, and everything was fine, until two days ago. My Intel Matrix storage manager gave me a notice saying a RAID volume is degraded because of failed hard drives. I turned off my computer, unplugged the failed drive, turned the computer back on. My computer then said the hard drive was missing (as expected). I turned off the computer again, plugged the hard drive back in, turned on the computer, and my computer said rebuilding RAID. It finished, and worked fine for about a day. The next day my computer told me the same thing, but a different drive. I did the same thing I did the first time, seemed to work again. Now, a couple hours later, my computer is giving me the same message with the first drive that gave me problems. Does anyone know whats going on?
Thanks in advance,
Cory

I don't really have the money to buy a RAID controller right now, so I was really hoping it wasn't that. Could it be anything else?