Usually browser based games run smoothly even to very old pcs... The only thing that can slow down them is your internet connection. Perhaps your Internet is too slow, and your browser's setup stop the screen loading after a while or you have some virus issue (but since you said you used several pcs the first one is more possible.)
When I say your Internet connection is too slow, I don't mean only your actual connection speed, but the connection between you and the server's location. If the "line" is overloaded can slow you down, or even if a damage to one of the lines occurs...
I remember once when due to some Italian military exercises, they cut the connection line between Greece and Italy, cutting us, for two days, from the rest of the world... We were able to join only what was to Greek servers or we could wait half an hour to see pages from other locations due overload...