According to the RISC OS 3 manual, resetting the CMOS by pressing "R" or "Delete" during a power-on sets the WIMP screen mode to 12 (640 x 256 pixels at 16 colours), the display sync type to composite (important for TV set compatibility, as I understand it) and the monitor type to 0 (old-style RGB monitors and TV sets). So if your CMOS RAM manages to keep those settings, they should be OK for you.

When I tried to connect my A3010 to a 100Hz CRT TV set, I found out that in order to actually get a picture on the screen, I had to tell the TV set to use the _RGB signals_ of the SCART cable, not YUV, "composite video" or whatever the other - inferior - standard is called.

The RGB->SCART cable I used had been built according to the diagram in the A3010 welcome guide.

You say it doesnt do anything at all now, don't worry. I opened my A5000 up and did something and thought that it had died. All you need to do to fix it is to give the mainboard a good clean and all should be well. Also push down on the ROM chips to make sure they are firmly in place.