Awful performance after trying everything

Solution 1:

That machine was mediocre even back in 2008 when it came out. It had an NVidia Quadro NVS 160M GPU (which you completely failed to mention) which was not really suitable for games even back then.

It will probably still make a decent machine for browsing the web or for office programs, but you seem to expect a speed daemon for gaming. That's simply unrealistic.

What are you comparing it against? What are your expectations? What did you measure, and how?

Do you have problems of the sort "it takes several seconds until a mouse click does anything" in the normal desktop? Or is it just game performance that you are missing?

Don't start tweaking BIOS settings. If you already did, do yourself the favour and revert everything to defaults. Unless you know very well what you are doing, you are probably only making things worse.

In all my 35 years of PC computing I have NEVER seen any useful documentation what all those crazy BIOS parameters (RAM timing etc.) do.