Just recently my laptop has started behaving weird. It often hangs after a short while of using it (perhaps half an hour), and memory usage is very high. I have 4 GB of memory, and after startup it often uses around 3.8 GB of memory.
This screenshot shows what processes are running and how much memory is used:
http://postimage.org/image/nk4muoxel/ I don't think I have installed any new software before this started happening, and I can't think of anything else causing it. My laptop is a few years old now and perhaps it isn't of the best quality, but I don't know if it's possible that some hardware problem could be causing this.