Asus G53jw showing only 4gb RAM instead of installed 8gb

Hi guys.. I am stuck with a bizzare problem.. three months back i gave my asus g53jw (i7-740qm, 8gb ram, gtx460m) to the authorised service centre here in chennai for removing a small block in one of the fans. The customer service was great but instead of fixing it, they changed the fans with new fans from Asus ).. laptop was great until last night.. I was using chrome, mozilla, photoshop, Visual Molecular dynamics(gpu heavy application) and Battlefield 3 at the same time. system lagged for the first time. So i checked the memory usage and was suprised that the system showed the total memory as 4gb instead of 8gb. I checked the laptop and all the four slots are occupied by 2gb RAM each. But windows shows it as 4 gb. CPU-ID software detects 8gb of RAM. what should i do.. have attached some pics for your referral!!! please help..

PS: BIOS also detects only 4 gb..

 

First I would reseat all of the RAM that is easily accessible. Then if BIOS still show 4 GIG, remove 1 stick at a time and see what BIOS reads. Once you get the BIOS to see 8 GIG, you should be fine.