As |The|Specialist has implied, a lot would depend on what the cracker was doing. I suspect that you mean "would I see anything"? rather than information from logfiles?

At best you might notice hard drive activity and modem activity from the flashing lights. You might also notice high CPU usage if you are monitoring this. This would only be of use whilst you were not doing anything, otherwise your activity would mask that of the cracker.

If your computer is switched on and connected to the network you are vulnerable to a remote attack. You do not have to be logged on. If you think about it, Administrators maintain machines remotely over a network when the users have gone home.........all they need is for the machine to be switched on and connected to the network.

Cheers