MPC500 Failed (514) system halted

After using my MPC500 without any problems for the last year it suddenly played up and refuses to boot. At first it got stuck on the first screen(MPC500 startup), now it just loads to to the name screen (MPC500 (128 MB)).
I've took out the 128Mb RAM and tried without it without success. After putting it back the RAM passed the tests.
I've tried to reload the OS 1.31 (Shift+power) but it gives this error message: FAILED (514) System halt!
After that I can install the OS using "erase+power", but problem remains.
Anyone familiar with this problem? Suggestions much appreciated.

open it up and check for loose connections and damaged cables.

The MPC didn't failed. YOU failed the MPC. You left him alone while you fiddled with the internet and now its payback baby. Feel his wrath as it creeps into your mind to the verge of insanity.

Thanks so far for the helpful suggestions.
I've had a look inside and couldn't see any loose connections or wires but this still might be the case.
The MPC starts up one or two times after a long period of time, say 12 hours plus. But then the problem reoccurs.
Sounds familiar to anyone?

I've read that you reloaded the OS, but did you mean you reinstalled it?

Sometimes a loose RAM can cause that, but putting it back in place should've fixed it. Check the pins of the RAM storage. Also check your compact-flash card storage maybe you pulled the card out too frequently and a bent pin is causing that.