Could be anything. I even occasionally have this problem outside China with Google or other search engines. Try to clean up your internet cache as I did; then it should normally be OK.

Three different caches on Windows for you to worry about I believe and you will need administrators' rights to delete them or contents therein. They can all cause trouble when browsing. Linux is easier with just one cache in 'hidden files' (windows also hidden) You just delete the whole file and it'll make a new one. I automatically delete the TV computer cache every day as it soon gets polluted by 'streaming video' IN China you should dual-boot your pc with Linux and windows and use Linux for streaming video and talking to your western bank on-line. Don't watch TV myself, prefer a good book.