It doesn't sound normal; but on the other hand, I'm not sure what would be causing it. The only thing I can suggest is to open up the service properties- there should be an option on what to do if the service fails-- you can try setting that to restart and see if that will keep you running. The project server was off for a while yesterday; and I noticed that 2 of my clients had died--they restarted OK though. Might also be worthwhile to completely restart the box and see if that clears it.