Which version of BOINC?
Which operating system?
Which project?

There's not much to go on, but it could sound like another problem. Some running the HPF2 project are having some problem with a long time between checkpoints. When/if they shut down, the job will resume at the previous checkpoint. If it hasn't made it to the first checkpoint, it starts over.

Is your original workunit there and running again, or is this a different problem?

Is the laptop getting hot? There's some throttling options to slow it down if needed. The BOINC throttle works for some, and there is a more complex product called Threadmaster.

Some of us just leave our computers running 24/7 to minimize the checkpoint problem, especially with HPF2. I can not yet verify this myself, since I am finishing up a few GC workunits. I have both HPF2 and FAAH workunits in the queue for later.