BEFORE YOU BEGIN, RECOMMENDATION:
Backup your data - I've seen this operation wipe drives instead of recovering data. Especially if your RAID controller and driver firmware/drivers are outdated.
When done, boot up your server, wait for RAID prompt, hit Ctrl+M (If I recall correctly). This will place you into RAID configuration utility. Select "View", choose the drive in question it should show up as "Offline" and/or "Failed". Look below at the screen, one of the options should be "Bring online".
Otherwise, if you have Dell OMSA installed, depending on the version you may have to do it either in Dell Open Manage or open computer management and expand disk management section. You should see Dell module plug-in which will show you your drives. Select the volume/drive in question, right-click and chose online. On newer systems same operation will be performed via Open Manage. Launch OMSA, login, expand RAID section and view options available - shold show your volumes and provide an option to bring drive online.
