low memory message

i have a simple E-Machine desktop with windows 7 Home Premium, 2 G memory and 64 bit system. i have no games, only one or two programs and use the unit primarily for Pandora and some photoshop. Every day lately, i get a Low Memory Warning and have to shut the comp off and restart just to even play Pandora music.
what could be the problem and how could i fix this?
thanks a ton in advance.
andy