CPU usage Problem, freezing mouse, chopping sounds

[linkerko]

Im having this chopping sound,Mouse freezing sometimes and my CPU usage is going 30-90% with 1 or few small application running. When I try to watch video for example in youtube, it cause a chopping sound and delay. Im not really a computer guy so im pretty much not aware in such things. Hope someone can help me and explain what should I do in detailed explanation.

My computer

dual core 2.50ghz processor
160GB hard disk
1gb memory
512 Video card
asus P5GC-MX GBL GREEN FSB1333 Mother board


Hope someone can helping.. I need the computer for my studies.. Its my exam week.. Y_Y