Yes it can very well be over-heating.
When you removed the processor you most likely failed to re-apply new thermal paste to the processor.
If this is the case, I would recommend removing the processor heat sink and cleaning off any old paste and applying a new fresh bead to the processor head and re-installing the heat sink.
This will probably reduce your core temp by 20 to 30 degrees.
Also make sure the heat sink is fully seated on the processor's core and level.
Let us know if this worked.
Edited by MrBruce1959, 23 May 2010 - 08:15 PM.