DELL 4500S problem

[only_lonely]

My delll 4500S facing the heat problem..it'll auto restart..
last week I felt that is CPU heat problem(is very hot at the CPU heatsink),pc keep resetat after work in winXP 30mins.
Then it suddenly OK,work normal for 3 days.
Now the rebbot problem occur again,but now is not the CPU very hot,but the northbridge heatsink very very hot.
what is the problem that cause the heat problem?

is anyway that i can obtain the schematic for this mb?

I really needs help.

my mb is out of warranty,n i wonder if DELL can repair it for me /charge me at high price service.