600XL Help

[ApolloBoy]

I just got my boxed 600XL yesterday, and when I hooked it all up, all I got was a blank screen. When I pressed Reset, it made a small beep through the TV like it was supposed to, but still nothing. What's wrong? I'm suspecting that either the GTIA or the RF modulator is dead. Please help me! This is my 1st Atari 8-bit, and I don't want it to die on me!

[ApolloBoy]

UPDATE: I've analyzed the PCB and all the chips, and several data address lines aren't working well, which makes me suspect the OS chip is dead...