I just acquired this desktop (used). It was running Vista 32 bit with 2gb DDR2 memory. I installed Windows 7 Home Premium 64-bit and everything works perfectly. I decided to increase the memory to 4gb. I installed 4 matched sticks of 1gb each (Infineon DDR2 667, DDR2 5300). It boots to windows and system information displays: 4.00 GB (3.75 GB usable). The problem is the sound is just loud crackling noises, the Network adapter fails and the video has problems. When I reduce total memory to 3 GB, everything works normal again. According to Acer, this motherboard should support 8 GB. I searched google and found another person that had the identical problem I am having. It was never resolved. I wonder if a BIOS update would help. Acer does not offer downloads of BIOS updates via the web for this model and they will not discuss this problem since the warranty has long expired.
I tried enabling "memory hole" in the BIOS but it did not help with the problem.
Acer Aspire M3100 / AM3100
Mfg Date: 2007 / 10 / 12
[edited for privacy]