Farms-gti

hi guys, was wondering if anyone could help me, ive got an escort gti and after running about 5 minutes i loose power to the head unit, the rev counter stops working and all the lights go dim, about 30 seconds after that the engine starts to splutter then cuts out. but turn the key back to the off position everything works fine again head unit, lights, starter engages and fuel pump primes), but the engine won't turn over and start until a couple of minutes later,then it happens again