Network sharing problem

We have a peer to peer network with 8 windows xp pc's. One of the computers on the network is having issues sharing documents. The folders that are shared on this computer will share for a while after a reboot but eventually the other computers will not be able to access the files until the pc is rebooted. This issue has recently developed, sometime in the past few weeks. The computer with the issue used to host the accounting database for our company and was accessed daily by every computer on the network with no problems. We moved the database to a newer computer a few months ago.