Windows recently released a fix for known memory issues in Windows (KB3065097)
The issue was Windows Updater grabbing most of the memory and never releasing it, thus slowing everything down. You can see it in Task Manager as Image Name svchost.exe burning all the RAM (make sure you tick the 'Show processes from all users' box.
I have a Windows 7 Netbook. I had turned my Windows updates off so missed KB3065097, once I'd applied it the problem was solved. I've also applied it to a customer's laptop which had the same issue and that worked too.
You can check to see if you have it or not by following these instructions;
Seeing which Windows updates are installed - Windows Help