It could be several things. If your OS drive is approaching full, that could slow things down as it needs to shift stuff around to find space. Your Windows installation (which version are we talking about?) could be suspect if it has been installed for a while (bloating due to updates/added and/or removed stuff/etc.). You might have a driver issue somewhere (graphics cards, older ones, usually come with driver issues or perhaps that's just my experience). You could try booting into safe mode and see if you get 'normal' performance in that environment. If you do, the problem is somewhere in your drivers or Windows installation. Instead of adding more RAM, make sure that you have plenty of room on your OS drive for Windows to play with (as a swap file, if that is still the correct terminology). For the type of use your describing, the end result should be the same.