Ugh Still having problems at boot under 10.5.5 and Mac pro

Question

Not sure what happened with the subject of my last post, but here it is again
So I had posted before my error that seemed to be a memory error on my Mac Pro (started with 4MEM), and I have yet to be able to reproduce it in Apple Hardware test. I have a Mac Pro Quad 3.66 with 8 GB of Ram from OWC in 4 2GB chips. I ran the test with all 4 in and also every possible combination in the machine.
After I boot the machine after running AHT, it runs fine. When I shut down and try and boot on its own, the screen freezes, draws funny, etc. Sometimes the screen looks snowy and flashes and I have to force restart. It also gets VERY sluggish. I don't know how else to describe that. Sometimes the icons in the dock don't draw right. I assume it is the memory because of that error the one time, but I can't reproduce it. Also, AHT only seems to test the memory and logic board now? Is that right? It used to do a video test with all the different color son the screen and test the other components. Does it no longer do this?
OWC said they'd replace the memory - if I can figure out which one is bad. Good luck.
I can't call Apple as my Applecare won't be here until Tuesday (I get a discount through work or I'd have renewed over the phone)
I ran memtest and member and it passed every time, though it was unable to lock the memory.
Any idea what might be wrong and how I can fix it?

Answer 1

Not sure how long it has been bad. I have known for a couple weeks as I had dusted out the inside of my machine with compressed air a few weeks ago and accidentally plugged it in to the wrong port. the computer was working fine then, so I let it go as something I'd eventually get fixed when I reupped my AppleCare.
I don't have the modem going through the surge protector at this time, but I probably should.
Now, since I have run Onyx, the computer boots up and seems to run fine.
However, every time I run AHT if the Ethernet cable is plugged in, I get this error:
4MEM/43/40000006: B: 1 C: 1 R: 1
If I run it with the Ethernet unplugged it passes every time.
That said, the first error code I got, was 4MEM/42/40000006: B: 1 C: 1 R: 1. I only got that the first time I ran AHT (which I mentioned in my first post) and have you to get that message again. The one with 43 I get every time if the Ethernet is plugged in and not at all otherwise.
It passes rember and memtest every time too. I just ran 2 more cycles of rember this morning.
It seemed I was having the 10.5.5 graphics issues many others were having and those seem to have been fixed by Onyx. Apple Care won't be of any help because this is all 3rd party memory I have in here (I do still have my original Apple Ram), but OWC won't replace any of it unless I can narrow it down to WHICH chip(s) it is.
So I am not sure if anything IS wrong aside from my Ethernet. It seems to be running smootly post Onyx. I am going to try a few restarts to see if I have any graphics issues. The guy at OWC suggested I take the memory to best buy or a computer store to see if they have a memory tester to find out if that is really the issue.
When Apple Care arrives, I'll get the Ethernet port replaced.
Any other suggestions?