First off install OpenManage as recommended above. Dell will ask you to do it anyway.
Secondly contact Dell and open a call with them, in all likelihood you will be needing an engineer or a new drive(s) at the very least.
I had the degraded error msg, what I tried first was removing the drive that had failed, then reinserting it. When that happens it should start a rebuild, you can check this in array manager. My drive actually came back and rebuilt 100%, but failed again in 2 days...turned out to be a faulty disk. Get advice from Dell anyway - no point in having RAID if you don't get on an error like this quickly...