the DRAM chips are U16 U17 U18 U19 and U110 U111 U112 U113. (MT48LC1M16A1) on the green boards.
i would try pushing on each one in turn and try booting up. maybe it's just a broken solder joint. the board flexes in the direction most known for breaking solder joints on surface mounted chips. if they were turned 90 degrees, it's not a problem. if you do find one that works when pressed down, you can TRY reflowing it. the pins are a little on the small side and prone to bridging if you don't use lots of flux. it may be best to get a professional to look at it.
check for spills, crud, corrosion around any of the chip legs. it's not uncommon to have stuff spilled into the cabinet, get on the board and start corroding things. look for scratches on the board that may indicate a slipped screwdriver or the like. check for solder pads on the backside that look like something may have been knocked off like a resistor or capacitor. if it never had anything there, it will have nice smooth solder bump... if something has been knocked off, it will be jagged or rough.
There are some components prone to getting bent and broken near the edge connector. (some resistors and transistors near one of the screw down holes) make sure things are all in one piece there too.
If you end up throwing in the towel on your board, I'm in canada and have a green board pulled from an old GT 2005 machine. i'm 99% sure it works, it doesn't have a video card (was robbed to fix another machine)...so you'd have to transfer the card and security chip bootrom and whatnot to it.
If anyone is willing to part with a complete board or just a replacement security chip please send me a message. Have had a complete board for last few years which I’ve nailed it down to a failed u53 (
unfortunately complete machines where the last of the series using that board before it got swapped to actual PC hardware (called the "nighthawk" system). So piles of complete system boards got sold off. because of this, so there are no "extra" security keys like there are with other years. (you replace the security key with a new one and load new software when you upgrade from one year to the next.) but in this case, a whole new system replaced the game after complete. so spare complete security keys are few and far between and usually only turn up when someone trashes a cabinet or a board fails. this is why you can find piles of 2002/3/4/5 security keys out there.