Many programs does not respond for a while after memory and SSD upgrade

Many programs does not respond for a while after memory and SSD upgrade

A few months ago I have installed an SSD and memory on my notebook. I also
started using Windows 8 and started having many programs going into 'Not
Responding' state for a while (sometimes up to a minute) then continue
without a problem. At first I thought the problem was Windows 8 and
installed the drivers manually, it didn't help.
I ignored it for a while then it became frustrating. Today I went back to
Windows 7. As you can guess the problem continues and I have no idea what
is causing it.
I had installed all updates in both Windows versions.
I replaced two 1GB chips with 2GB ones(same mhz)
It's a Dell Insprion 1520
Any idea why would it happen or how I can diagnose this problem?