Random BSOD's - Two different Messages

[Eddogegr3]

1. system_service_exception (tdx.sys) 0x0000003b
2. pfn_list_corrupt (no file listed) 0x0000004e

Computer: Dell Dimension E521 (Desktop), with 4GB RAM. No Video Card.
OS: Win 7 Professional 64-bit. OEM version from Newegg.
Computer originally came with Vista 32-bit. BSOD's did not start until a month or so after Win 7 64-bit was installed.
Diagnosis steps: New Nvidia drivers installed for on-board video; New Memory sticks; neither step stopped BSOD's.
Antivirus: Newest version of Avast (Free, Home edition)
Other notes: The crashes usually happen when someone is on the computer as best we can see. They are very random otherwise. Pandora gadget is often played in the background with MS Office Open, Act by Sage, Chrome, Google Talk, those are the most active running tasks. It is not on Wifi, it is on Network directly through on-board NIC.

I have attached files per instructions.
Thanks for any or all help in advance!

 

[zigzag3143]

Related to tdx.sys (an OS file) Please run this system file check

Run a system file check to verify and repair your system files.

To do this type cmd in search, then right click to run as administrator, then
SFC /SCANNOW

It may need to be run up to three times before successful
Let us know the results from the report at the end.

Read here for more information http://www.sevenforums.com/tutorials/1538-sfc-scannow-command-system-file-checker.html

 

[Eddogegr3]

I just completed the scan and it said something to the nature of "No Errors" or no file integrity problems. I appreciate your quick response. Would there be any other suggestions? Should I provide more information?

edit: Yes, I did run as admin for the scan.

 

[zigzag3143]

I just completed the scan and it said something to the nature of "No Errors" or no file integrity problems. I appreciate your quick response. Would there be any other suggestions? Should I provide more information?

edit: Yes, I did run as admin for the scan.

Good news on the SFC

I notice your avast which is often at least a contributing cause of BSOD'S . Please remove and replace your Avast with Microsoft Security Essentials AT LEAST TO TEST


http://files.avast.com/files/eng/aswclear5.exe

Microsoft Security Essentials - Free Antivirus for Windows

 

[Eddogegr3]

I just completed the scan and it said something to the nature of "No Errors" or no file integrity problems. I appreciate your quick response. Would there be any other suggestions? Should I provide more information?

edit: Yes, I did run as admin for the scan.

Good news on the SFC

I notice your avast which is often at least a contributing cause of BSOD'S . Please remove and replace your Avast with Microsoft Security Essentials AT LEAST TO TEST


http://files.avast.com/files/eng/aswclear5.exe

Microsoft Security Essentials - Free Antivirus for Windows

We went ahead and did a remove of Avast and a reinstall with Windows Essential Security. Today was really the first full day of use and we just saw the first BSOD. It was the system_service_exception (tdx.sys).

What would you recommend for the next step? Thanks again!