|If you haven't already done so, the 1st thing I would try is updating the BIOS, especially if your current version is 1602 or older.|
Other than that, you have several options, none of them pleasant:
- stick to 2GB RAM
- try a PCI ethernet card...it seems to work in some cases, but not all
- install a 32-bit OS
- get a new motherboard
There are some tips in the following article...scroll down to the comments & start with #7:
And just FYI, running 3 sticks of RAM will knock your system out of dual channel mode. If you wanted 3GB total, it should have been 2 x 1GB + 2 x 512MB rather than 3 x 1GB.
Also, if you're not overclocking the CPU FSB to match the RAM speed, the RAM should be underclocked to match the CPU FSB. Manually configure the RAM settings in the BIOS to run as DDR2-533 (266MHz frequency) & also manually set the memory voltage to the RAM manufacturer's specs...do not rely on AUTO settings.