Dimension 9200

Hello all

Tell me if I'm banging my head against the wall, I'm numb.

My 2 year old Dimension 9200 would not turn on about a month ago. I didn't have a power supply tester but, having seen this in other Dell's, I swapped out the PS. No good still dead. I ordered a refurb'd MB from an ebay seller. Installed, turned on, everything loaded and worked except would not pass any data through the serial comm port. (I specifically need that to work for one special app). So I return that one for a 'new' board ($20USD more) from the same seller, that board goes in, everything works at first then the system starts freezing, no rhyme or reason, no pattern, no response to KB or Mouse, has to be shut down and rebooted from the front on/off switch. CPU temp is fine. So that Board goes back and is exchanged, next Board in the saga works BUT all communication involving the NIC/LAN scrambles every page loaded in any browser, http code shows up and email operation is inconsistant, drops connection, doesn't connect, then does etc.

I am just going to have to put down nearly $400 from Dell to get this right?

I've built units from scratch and been into electronics for 40 years. I've done all the usual trouble shooting from running this barebones to fully loaded. 2 of the three boards had no express service code, the last one, supposedly New, did. I am just dealing with the wrong vendor? These guys have near 20,000 feedback of nearly 100%

My thanks to all who take the time to reply.

doc