heya Pie zancudo
Well if you tried everything I can only leave you something that worked for me, weird but real. when you open the runescape wait for everything to load normal, do not close the page and try to open another window of RS without closing the main then on the second page try to enter your account. I had the same mistake and I do not know why it works on the 2nd and not on the first one. After you enter you can close the first one you opened.
if that does not work, I suggest you activate all the cores of your processor and the entire RAM card then uninstall the game, restart the computer and reinstall it.
I hope to help you and have fun!^^
Skiller level 3
Sorry for my english :3