Very High RAM usage very low CPU usage, fix?

Hi!
Recently I did a clean install of Windows 7 home premium and as soon as it completed I started noticing unreasonably high usage of RAM while having little to no CPU usage ( out of 16GB total RAM the portion that is usable jumps from 2GB to 256 MB)
I tried goofing around with the boot options in MSCONFIG and set it to use all 4 compute cores and no maximum amount of RAM. After restarting several times I seems there is permanently only 265MB of RAM usable and my PC is barely usable at this point. I'm only 15 and I have very little experience in this sort of stuff so please try to dumb it down for me. Cheers x

Thanks for the reply!
While this did help, it only freed up about a 1GB of RAM, and that's after I disabled the NETGEAR A6210 Genie and Steam programme that launch immediately after boot. After going through task manager I noticed that the real memory hog program is 'svchost.exe (LocalSystemNetworkRestricted)' and 'avguard.exe'. Any idea on what would hell reduce that memory usage?

I'm not sure what any of that means. If it helps to know this PC was bought to be used primarily for gaming.

When I uncheck those boxes you circles in red the startup switches from normal to selective, is that a problem?

Having tried restarting with both selective boot with nothing checked and normal boot with everything checked I've found there's zero change in RAM usage and it stays like this:

This PC was bought as it is now, the only things that didn't come with it are the monitor, mouse and keyboard.