Bad video memory

I have an Acer x1700, with 4gb of Ram, 2 hard discs, running Vista Home Premium. It has worked flawlessly for years. Recently it started hanging. No mouse movement or keystrokes had any effect. Had to shutdown by holding power button for 10 seconds. Got more frequent until now it only lasts a few minutes before freezing up. Thought it was a virus or malware, but ran Avast and Superantispyware and Kapersky with no errors (except minor adware). Removed all of that and still no joy.
I ran the Passmark burn-in tests. Everything checked out except it gave continuous 2D graphic errors, and could never access the video memory. I had a GE Force G100 512 mb DDR2 DVI/HDMI board installed. Removed it but got the same errors just using the onboard video.
First question - Does the system use the onboard video memory (which I thought was just a part of the RAM) even when a separate video board is installed?
Even if it does, since the memory proved to be OK, using both Passmark and another RAM tester, is there separate video memory on the Acer motherboard, and is it accessed by both onboard video and graphics card?
Also, can onboard memory be replaced, or is motherboard fried?
Good little computer otherwise, and will upgrade with a total new system, but would like to fix this one up for a grandkid if it can be saved.
All help appreciated.

 

You should first run the DirectX Diagnostic Tool - dxdiag.exe. Click the Display tab and ensure DirectDraw, Direct3D & AGP Texture Acceleration are all enabled.

 

Oops. You are right. Ran the test and none of them are enabled. However, I don't know how to enable them and cannot stay online long enough to download it from Microsoft. If dxdiag.exe ran, shouldn't it already be installed?

 

It seems somehow DirectX has been corrupted. You will have to re-install it. I suggest you download and install DirectX June 2010. This is an update for Windows XP, Vista & 7. It is a 95.6 MB download. If you cannot stay online long enough, ask a friend or colleague to download it.

https://www.microsoft.com/en-us/download/details.aspx?id=8109

 

Will do. Thanks for the info. Once again, this site comes through for me. Appreciate it.