hi
From the data that fetches from the serial number you gave is that you have a Mac mini "Core 2 Duo" 2.26 (Late 2009).
The apple specs states that it can only support 4GB(2 X 2GB) of RAM but i have read on some websites that it can support 8GB(2 X 4GB) of RAM not sure about that.
But as you mentioned after installing the old RAM back it didn't worked, For this i would suggest you to recheck if all the connectors and the RAM is been seated properly.
If you still get the Beeps please explain the nature of beeps as for RAM error the beeps wold be something like this BEEP BEEP BEEP a Pause BEEP BEEP BEEP ie 3 beeps and then a pause then 3 beeps again and it continues.
if the beeps are not in this fashion then its some other issue and you have to tell us how the beeps are.
If you think i answered your question please rate (score) and mark it accepted. :)
Thanks