I got a pc re-assembled from used parts. The computer is P4. The computer works for about a week time. When computer is started (on) it does not give any display although it had been properly shut down last time. The computer assembler changes the ram and it works again for about a week time but the problem is again repeated. At first the ram was 1GB and afterwards it was replaced with 2 number rams each of 512 MB. Please let me know what is the problem and what is the remedy for it.