RAM no longer working, despite compatibility correctness

GamerJ98M

Commendable
Sep 14, 2016
14
0
1,510
Bought new motherboard and new RAM. Combined old RAM with new RAM, PC won't boot up. Only one RAM stick works and that's the new one I bought, when the others are in the PC doesn't boot up. But the RAM sticks worked on the previous motherboard and both the new motherboard and CPU specs say they are compatible...so why would they not work now?

Regards
GamerJ98M (James)

UPDATE (16:49):
Put in one of the old sticks into the third slot (motherboard has 4 ddr3 slots) and PC booted up so I guess it was a RAM compatibility issue...

I tested my third RAM stick in several places (ie. First slot and a working ram in 3rd etc) but nothing works so i guess that particular stick is defective/broken??

Is it possible to combine 1333mhz with 3 other types eg 2140mhz + 1600mhz etc...or do they have to be in pairs?