Steam keeps crashing every few hours when online...?

When I run Steam online, it seems to crash every few hours. This doesn't happen while playing games offline or online, or when I'm just leaving it there online, but when i'm checking up on my downloads and browsing the internet at the same time. The symptom is that a windows bar surrounds steam and when i click anywhere on the program or try to exit out of it, it it says "steam has stopped responding". I usually just shut it down and restart it, but this can get annoying. Any help would be appreciated, especially if its from experience!