I can't do English searches anymore.
As of 1.0.7, English searches are, by default, done by turning off JLookUp's IME. This can be done by pressing CAPSLOCK.
If you came from 1.0.6, you may have the 'Convert ROMAji to Kana' button checked. If you are using the IME, do most definitely do not want this checked; it will cause you to do Japanese searches almost no matter what.
JLookUp crashes on startup
Delete Options.jlreg and try again. You may have some corrupt or invalid options in there.
Delete any .jli files and try again. They may--for some reason--have indexed wrong. Versions after 1.0.5 tend to rename the index file format to force you to regenerate the indeces on upgrading, just to be safe.
You may need some fonts. JLookUp versions up to 1.0.5 all need MS Gothic to run. Sorry about that; it's fixed in 1.0.6 and up.
I can't see any Japanese
Get 'Arial Unicode MS', and have any areas that display Japanese text use that font.