My system not starting once in a week after cleaning the ram it is ok?

i had asus with p4 2giga configuration. my problem is it is not starting every four or five days. i mean no display. once i removed the ram and clean the slot and ram and put it in the slot then it displays normally and it will automatically goes in to bios and shows these message. your system processor speed has been changed. so it is started with safe mode. after that it will works normally. after few days it did not started. again i opened the cpu and clean the ram and i put it the same slot or another slot then it is shows the display and goes to bios and same above process. i changed the ram and cd rom also. but i dont know the actual problem. and also in the os ie. windows xp in the ide or secondary channel it does not shows the DMA access if possible option. is the facility does not in the mother board or p4 2.00 giga processor. if any antivirus installed then it will take lot of time to take startup and shows in the task manager the processor usage is 100 percent.