high cpu usage new computer

Hi, First time poster, I bought a Compaq SR5413WM about 4 weeks ago. I
use it for Voip based applications, light browsing and some printing.
Everytime I open IE7 the cpu maxes out at 100% and then bounces up and
down erractically, it also happens with other applications such as
windows explorer. I have a AMD LE-1640 2.7 ghz processor, 2 gb ram and
Vista home premium 32 bit. I have no idea why it is doing this, I have
searched the forums and can't find exactly the same thing. I hope
someone can help me.

Thanks


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mellieg68