Network/Internet Access Hangs After Few Hours?

I typically use Google Chrome for browsing, but I also have Firefox installed. I rarely use IE but that seems to be affected as well. Basically, after I've been using the computer for a few hours, all network access seems to die until I restart my computer. Furthermore, I sometimes cannot terminate all of the chrome.exe processes (an access denied error pops up from the task manager), and once the network has died, Firefox will not run (the process does appear on task manager but no window opens). Other network-dependent services also fail. The router I am connected to is working throughout this as tested by another computer and WiFi devices. This problem goes away with a restart 100% of the time. So far I have run scans with Security Essentials, Malwarebytes, and AVG. I was concerned there may have been a conflict between these so I have uninstalled AVG but the problem persists. I have uninstalled Chrome and Firefox completely (using Revo) and reinstalled but the problem persists. Unfortunately my oldest System Restore point is only about a week old and the problem has been happening for longer than that. I have disabled all extensions in Chrome but the problem does not seem to be isolated to one browser.

Here is my system info:

Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows 7 Ultimate, Service Pack 1, 64 bit
Processor: Intel(R) Core(TM) i7 CPU 920 @ 2.67GHz, Intel64 Family 6 Model 26 Stepping 5
Processor Count: 8
RAM: 9207 Mb
Graphics Card: NVIDIA GeForce GT 220, 1024 Mb
Hard Drives: C: Total - 597621 MB, Free - 184586 MB; D: Total - 12755 MB, Free - 2295 MB; G: Total - 953866 MB, Free - 321465 MB; J: Total - 953866 MB, Free - 89965 MB; N: Total - 1907726 MB, Free - 618964 MB;
Motherboard: PEGATRON CORPORATION, TRUCKEE
Antivirus: Microsoft Security Essentials, Updated and Enabled