I've done all that . . . more than once. JavaScript IS enabled.
Bird,
I recall reading somewhere that on W-8.1 you can make a particular site like W-7 compatible.
I didn't pay attention since before that applied to making old software work on newer versions of windows, not changing IE to work like an older version.
The windows 7 browser was updated 2-3 versions in its time.
I have updated my W-7 computers to the IE 11 browser over a week ago and it works fine and is faster than IE 10.
Don't know about the effect on your Java Script problem though.
Have you tried installing Chrome on your new pc to see if it will work with the Java script at your credit union?