My Laptop vs. Desktops

I've been using a laptop for about the last five years now. I like the convenience of it, but for some reason, I don't think they are as durable as a desktop. The last laptop I had stopped being efficient because the fan burned out and the computer would overheat and shut down every half hour. So since I bought a new one, I hate leaving it open because I'm afraid of wearing the fan out too soon. With a desktop, they're built to be left on all the time while only getting shut down every so often. So I'm currently looking for a desktop to complement my laptop. I like to be able to leave it on so all I have to do is sit down at my desk and start working. Sometimes, it takes my laptop up to five minutes to start up because it does not have enough memory to efficiently run Windows Vista. That just irritates me because it came already installed. If it's already on the computer, they should at least have included enough memory to run the program without slowing the entire computer down.