amd thunderbirds have 2 types
one burns out at 90c, other burns out at 95c
you can find this info on their website.. nothing to worry about tbh
i'd say you're computer is bogged down from misbehaving software.. also
your psu does seem somewhat underpowered

to those who say "check if everything adds up to 300w"
go die because you count by rails not by watts
a 300w psu with good rails can be better than a 400w psu with crap rails