The Battlescape client if more heavy for your PC to run over OSRS, some people are just generally unable to run the 117 HD Plugin due to this with their older hardware, however there are a few methods that can be tested prior to calling it a loss;
- Close all clients,
- Load up a fresh client (only 1)
- Toggle the 117 HD Plugin On/Off a few times (unless it works at first)
- Leave it toggled on, and refresh your client, this should be good to go.