Logging onto the network

I am the tech coordinator for my school building and I have a laptop that I take home each night. I unhook the laptop from the network cable each night, but when I come in the morning (some mornings later than others) I cannot get onto the network/server.
However, if I shut down and boot back up after a couple of hours, I can get on. Is this because there are too many people on the network?? Is there anyway to correct this?
THanks in advance
Pete Hunter