computer restarts by itself

[demultiplexer]

can a computer make restart because the memory cards arent the same ?

i have a GIGABYTE 7vrxp and 512 mb 333 mhz generic

256 333mhz 2-2-2 crosair

256 333 mhz generic

the computer restarts almost every 10 minutes when 2 of the cards are connected but when i work with one card only the computer works fine/

whats the solution ?

thanx

demulti