Run an ePSA diagnostics to see if it can detect any hardware issue.

Edit:  some how missed the info that a diagnostics did not detect any issue.

I discovered i have memory issue but is hard now how to check which module are failing.

I had 16x8 Dim Installaed and for the momente i have reinsalled 16x4 module and if i add the remaming 4 module i got 3 beep error on boot. 

Now for the memory matrix rule i can not add the remaining module one by one....so how i can discovered how many modules are failing?

You should be able to test each pair of modules until you get the error, then you can test with just one module to identify the faulty one.