ASUS P5NT WS and memory troubles

Hello.

I'am worried, that i'am encountering a serious problem with my MB.

I have 4 DIMM Slots (A1,A2,B1,B2). Normally i used two kits of 2GB (KIT 2x1GB) DDR2 800MHz PC6400 A-DATA Extreme Edition Vitesta = 4GB in total.

After i installed my new CPU cooler, i realised my system only running with 2GB's of memory, while all 4 ram modules are in MB. After trying all the rams/slots separately, i found out that slot A1 and A2 is not working at all - doesnt matter what RAM i plug in. (only A2 slot is working randomly - 1 of 10 tries)



Now only thing i can think of is damaged MB.



MY SPECS:
MB: ASUS P5NT WS / nVidia nForce 680o SLi Hybrid |
CPU: Core 2 Quad Q6600 - 2,40GHz |
RAM: 2x 2GB (KIT 2x1GB) DDR2 800MHz PC6400 A-DATA |
GPU: 2x MSI NX8800GT-T2D512E-OC |
HDD: 2x SEAGATE Barracuda 7200.10 500GB, SATA II NCQ 16MB cache |
CPU Cooler: Noctua NH-U12P |
PSU: Enermax Infiniti 720W ATX2.0 |
CaseFan: 2x Scythe S-FLEX SFF21E, 1200rpm, 49CFM |

/sheira

I dont think i have warranty, since i bought pc in "1 piece".

So basicly, there is nothing i can do? Is it safe to use other 2 slots this way? (so i can buy 2x2GB kit)