Help a Rookie? GP and CEL, can't read codes

First TDI, 2002 jetta (alh I think), nearing 300,000 mi. automatic. it's flashing the go and cel lights. we had trouble starting it up for a while, mechanic said it was definitely the gp not working, so we replaced the whole set. previous owner put in an aftermarket radio, so we can't read codes. cel was still on, so we took a guess & changed the maf sensor too. car has plenty of oomph now, but died on me once. usually I can figure out what's wrong by reading the forum, but we're stumped this time.
looking for a oem radio, but no dice so far. help a girl out? please?

At the very least, find a generic OBDII code reader and scan the car to see which code(s) set. Other than that, you're throwing expensive darts at a moving target.

Most AutoZone type locations will scan for free.

Alternatively, post up in the East U.S. forum and see if there is anyone close to you with VCDS who can scan your car: http://forums.tdiclub.com/forumdisplay.php?f=33

Take the radio out, it may or may not be related to your problem, but at least try and rule that out.

Flashing GP light usually means something more like a quantity adjuster in the pump.

You likely never had a glow system problem. But you need to get the car properly scanned.

I have codes, I have a reader, but the reader will not read the codes. I replaced the turbo, runaway acceleration is no fun. I replaced the injectors, still the original and horribly clogged. Also replaced the MAF sensor and a temperature sensor and the glow plugs. I average $200/month in repairs. I have no car note, so this is my tradeoff. I realize that I'm throwing expensive darts, but if I can't read the codes, what else can I do?
The car stalled out on me today. As long as I gave it plenty of fuel, it ran, but the minute I let up, it would try to stall. I know I'm asking for blind guides, but an idea of things to check would be helpful. thank you guys

Ya, your gonna average a lot in repairs every month if you cant scan it. Do the aftermarket radio fix from the following link, then you and your mechanics can scan it.

http://www.ross-tech.com/vag-com/aftermarket-radio.html

You need to find out why your scan tool cannot communicate with the car. Try a different tool, or as I already suggested since you said it has a non OEM radio, take that out and try again. You may have a cluster problem or something, tough to say. Could also have a shorted CAN bus wire in one of the modules, too.