If the system is set up with a RAID 0 array (two drives striped together), recovering the data will be very, very difficult -- if you need the data, contact a data recovery service such as www.drivesavers.com. The cost will be high, but they should be able to do the recovery.
Dell doesn't do data recovery. Chances are, what has happened is that one of the two drives in a RAID 0 array has gone bad - when that happens, all access to both drives is lost. If you really need the data back, you're about to be faced with a cost of well over $1,000 for data recovery.
The replacement of the drive(s) will not be expensive - data recovery, however, is.
OK Thank you for helpful replies