Computer gets hengd up any time suddenly specially...

Question

My Computer gets hengd up stop working suddenly, Mouse can not move specialy when I open Messager like skype or QQ Messnger for chating and also get hended up when open site for stock trading soft ware provided on line by broker, Computer power on but we can do any work Mouse can not moved at all its stoped to work and then again we have re-start pls let me know what todo???