1| When you post a thread that pertains to troubleshooting, it's customary to include your full system's specs. Please include your OS as well as the chassis you're working with.
2| I asked for the chassis since there is a slight possibility that your system is suffering from a grounding issue within your case. Try breadboarding it and see if the issue persists.
3| Since you're having to press the memOK button it means that your ram timings are off. The button tells the ram sticks to boot into default(lowered timings and frequency's) for your system to bootup. The next time your system boots up, go into BIOS and manually input the details of your ram stickers in their appropriate fields.
4| Have you made sure your BIOS is up to date?