Does it restart as soon as it powers up? If so, a marginal power source can cause these sort of behavior (a very discharged aircraft battery), but it's also possible that some fault has developed with the unit. If you have the internal backup battery, try disconnecting it to see if that makes a difference.
Also, if you actually have an original EFIS-D10, note that we are usually unable to repair them due to lack of parts for the original model. They are also all long out of warranty at this point. However, we do offer a flat-rate upgrade in these cases which turns your EFIS-D10 into an EFIS-D10A, with a fresh 3 year warranty. See http://dynonavionics.com/docs/support_discontinued.html for details on this program.