I can try to fix a few problems together with you.
First delete all your temporary (offline also) files and cookies, delete all stuff on your pc you don’t need to receive extra internet speed.
Re-install the newest JAVA.
Try when you chat to turn off all programs you don’t use to have extra chatspeed, the room shouldn’t be blank after minimize then.
About the scroll thingy.. I really don’t know. Perhaps it is your internet settings, that blocks scrolls on windows without buttons and adress balk. Try to see what you have set and try to find a setting that could cause this problem.
May you still have problems after this all, send me a PM with your JAVA console at the moment you are chatting, you find your console in: Extra > Sun Java Console. Copy this to me.