Memory Doesn't Get Freed; System Functionality Decreases

I have 8GB of memory in my computer.When I power it up, the memory usage starts out at somewhere between 10%-20%, which I think is OK.After a while of using the computer and opening & closing programs, the amount of memory being used steadily increases, until it escalates to around 89%, upon which things start to work poorly.The most prominent effect is loss of internet connection.Network stops working entirely, and running ipconfig shows nothing, as if I don't even have a network adapter.I tried opening the Network and Sharing Center and the Device Manager when this happened, but they wouldn't open.Also, it is difficult to restart the computer after this starts happening.The computer seems to be working swiftly, but certain actions seem to be problematic (e.g. opening Task Manager or any Explorer window, or reaching the Ctrl+Alt+Delete screen). Other things might still work, though (for example, opening Command Prompt).

There is no error message of any sort, nor a BSOD.I can somehow understand why this might happen, if no memory is available to the OS, but what I don't understand is this: Even at 90% usage, with 8 GB of RAM there should still be enough for the system to operate normally.Why does closing programs have no effect on the situation?I summed up the memory taken by all open processes when the memory was at about 75% usage, and it doesn't even add up to 2GB. Adding an exaggerated 2GB extra for the OS itself, it shouldn't even reach 50%.How does this come to be in the first place? It looks like closing applications does not free the memory they were using.I performed a full virus scan using ESET's online scanner (in case my own antivirus was compromised), as well as a malware scan using Malwarebytes' Anti-Malware, but everything seems to be clean.I've had this computer for around 3 weeks, and have installed mostly games on it so far.Basic System Information:Operating System: Windows 7 Home Premium OS Version:6.1.7600 Build 7600 System Type: x64 RAM: 8 GB (2 x 4GB) Antivirus: NOD32I've attached a few files with some more information: System Information.txt - Exported from msinfo32.Resource Monitor Numbers.txt - A summary of the information in the Resource Monitor when my memory was at around 75% usage, before the functionality issues start to occur.It contains an exaggerated sum (rounded each value up to the nearest whole MB) of all the process memory values in the Processes table.IPConfig.Bad.txt - What running ipconfig looks like after the functionality issues start to occur.