My my cpu has just started overheating

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The cpu in my secoundry system for no apparent reason has just started overheating, I have'nt changed anything at all, checked the cpu fan speed etc and is fine, the system just kicked my mate off of farcry with a cpu temp of around 75-80 and even taking off the side of the case the temp was hovering around 60-65 idle , my secoundry system specs are as follows,

My first instincts was it may be the psu, could this cause my cpu to overheat ?

P4 3.06 northwood
intel m/b 850E
1 gig rambus 1066
550W QTEC PSU

thank for any help.

 

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afraid it's not dust, I keep my system air dusted on a regular basis

 

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gota go to work, , will try that tonight, cheers