Welcome back! What sort of stuff did you work on back in the day?
Assuming a process hasn't crashed, try using the "status" command from a CLI, followed by "break [process number]". Exchange (in SYS:Tools/Commodities/) can shut down some tasks as well. If it's a GUI program, the close gadget should suffice.
You can detach processes from the shell by preceding the command with "Run >NIL:". "Run" to detach it, and ">NIL:" to squash any output you don't want.
There probably hasn't been any good Amiga-related printed material since the early 90s. There's an Amiga books FAQ kicking around the web which might be useful.
Denny Atkin's book might be a good reintroductory tool.
Also, pop open the machine and make sure the battery hasn't started leaking.Feel free to ask if you need more help.
