Laemeur

Howdy, folks. I picked up an 800XL a few days ago that had some problems. The first problem was a few bum keys, but that was an easy fix since they were all on the same line of the keyboard membrane, and I just used some foil and transparent tape to bridge the broken part of the circuit. The second problem was that the video was having a hard time staying one color. BASIC would go from blue to green, sometimes brown or yellow, even. I poked around these forums for a bit and saw that re-seating chips was a common recommendation for video problems (as well as checking the power supply, which I haven't done yet), so I popped the top and reseated just a couple chips to make sure I knew what I was doing. I powered 'er back up and everything was working, except the video was still having trouble keeping its color. With the power still on, I started (unwisely, I'm sure) just sort of pressing chips down into their sockets to make sure they were well-seated. I got to one of the smaller chips in the column of chips on the left (I assume these are memory) and the video sorta went wild on me for a second, then blanked. I switched 'er off, thinking I'd killed the poor thing then and there, but then I switched it back on and - viola! - BASIC came up in a nice, steady blue. Never one to quit while I'm ahead, I turned the power off and continued to just sorta press the rest of the chips into their sockets like I had been doing before (just for thoroughness' sake, of course). Only, after I'd finished doing that, I switched the computer on and... no BASIC. The screen, after switching on, flashes white once, like it's always been doing, but rather than going to the READY prompt, it just blacks out. I have since gone back and properly re-seated all the chips, but the symptoms haven't changed. Does anyone have a suggestions for what I can/should try to do next? Thanks for any and all help.