My system memory drops from 4gb to 2gb????

so i was overclocking my graphics card recently and while checking to make sure my overclocks were applied using evga OC scanner, i saw that it recognized i had 2gb of RAM. I checked the properties of "My Computer" and it said 2gb of RAM. I updated my beta profile on blizzard and their program said I have 2gb of RAM. I've been very busy the past few days so i have not had the time to take my computer apart to check it but i wanted to see what you guys think first? Does this pretty much mean one of my sticks has died, came loose in the socket and isn't connected, mobo problem or what?
 
first of all open up the case and check to see a stick isn't loose (don't understand how you don't have time to do this but do have time to post about it), if that's not it then try each stick individually to either confirm they're both working fine or find out which one is dead (if that's the case).
if you still have the problem THEN you post...