You shouldn't turn the machine on and off repeatedly. It stresses the electronics and can cause premature failure of some of the components.

check voltages and try re seating the ribbon cable for display board

does the cpu leds act normally at start up ?
like a glimpse of pia led and then go to light blanc led and remain on !
the middle led should stay on all the time ( is 5 vcc test )

check also power supply connector 5 Vcc to cpu
sound robocop at start up can be heard without a good boot of the CPU !

Sounds like you could have a grounding issue. Data East games are notorious for this. Here is a great guide for Data East repairs (see section 3c.). Good luck!

http://hansbalk.home.xs4all.nl/rep/ds/index2.htm#reset

More info from this article quoted. Check this easy fix first:

"Random Game Resets On JP, LAH and TftC.
During game play, the games Jurassic Park, Last Action Hero and Tales from the Crypt randomly reset. This occurs beacuse the +5 volt line is shorting against the ground backbox metal plate. This grounding plate lies behind all of the printed circuit boards mounted inside the backbox. The metal plate can bow, causing it to intermittently short against one of the backbox circuit boards. This will cause the game to reset. To fix this problem, remove all the circuit boards (label the connectors!), and remount the metal backbox grounding plate to remove the bow. Another solution is to remove the sound board and affix an insulting material to the metal plate directly behind the sound board at connector CN2. This will insulate the metal grounding plate from the sound board (which is the board most affected by this bowing metal plate). Make sure the insulating material is non-conductive, and thick enough so it cannot be perforated. This problem was discussed in service bulletin number 55."

You need to do as doctor_pinball suggested. Look at your CPU led's. Follow the directions on this link:

http://www.pinwiki.com/wiki/index.php?title=Data_East/Sega#Data_East_CPU_Board_LED_Flash_Sequence

It will tell you what the led's should be doing. Try to catch it with the problem on boot up. But if you can't catch the problem on boot up and it will only do it after playing for 15 minutes then look at the led's when the problem occurs. Then report back what you saw with the led's.