Windows Explorer and now Browsers slow / timing out

These two issues may or may not be related, but both seem to have started recently:

1. Windows Explorer (not Internet explorer) just sits there for ages (several minutes) before actually displaying the contents of my computer. The structure on the left is all there but the right side where all the files should be is just blank with a swirly "processing" cursor. Strangly, if I go into an application and do file>open I can browse instantly around the computer in that browse window (while explorer is still sitting there like an idiot doing nothing)...
2. In multiple browsers (IE/chrome) I'm getting a problem where some websites are working (confirming there internet connection is ok) and some are timing out. There seems to be no pattern as to which work and which don't and I've just noticed something that makes me think it's related to the first problem - I try to open website A but it keeps timing out. I try a couple of other websites, they work fine. I find another website (b) that doesn't work. Several minutes have passed since I tried website A so I try it again - it works! website b still doesn't work. I wait a few minutes and try again - it works!

So in both cases it seems to be searching for something and not finding it, then it eventually finds it (or times out) and then it all works...

Any ideas where to start with this...?

win 7 pro; 6.1; build 7601 sp1;