computer freezes and I have tried alot......no luck

Hi everyone, new to tom's but have seen a lot of good info since finding this site.
First of all, I am self taught at running a computer, so I am sure I missed a lot,
but I am still always learning and could use your valuable help here, I am totally
stumped.

I have a:
Gateway GT4016 pc with AMD Athlon 64 Processor
3700+, 2.21 GHz 1.00 GB of RAM

My system is:
Microsoft Windows XP Media Center Edition
Version 2002 with Service Pack 2
(can not download SP3 with out loosing internet)

My Graphics card is:
ATI Radeon HD 4600 Series

For about a year now my comp will freeze when I game during the day, at night when
it is cooler I have hardly any trouble. Now I experience freezes when I run
streaming videos during the day, at night it seems fine. I have updated and updated,
reformated and reformated. Though I am still trying to update graphics card yet again.
Still I am having the same problem only worse now. I recently installed Speccy and
know what my temps on my hardware are.

Here is my day time results:
(temp. here in house is around 84*F during day and around 60*F at night)
Speccy results
------------------not gaming---------gaming
CPU -------------67*C - 70*C-------108*C - > freezes
Motherboard -----40*C steady-------40*C
Graphics---------45*C - 47*C-------59*C
Hard Drives------368C - 37*C-------36*C

I also have installed Speedfan and it gives my CPU at 88C - 91C not gaming and 127C
gaming. Speedfan only gives one fan when I know I have two running.
Why am I freezing and what can I do!!!!!

Just a note, I am disabled and live on a very fixed income, so putting a lot of money
into my computer is sorta not in my future. So any help will be most appreciated being
this is my only link pretty much to the outside world.
Please help!!!!!
hopelessly
kymrobbins