did you upgrade to 64bit Os or is it still 32bit?
are all your drivers up to date? (especially for mouse,sound etc)
My main concerns at the moment are
Your Hdd size
your ram amount
your graphics card
I wouldn't even look at overclocking the rig until you can upgrade those components imo
The headphone issue seems like a loose wire to me or a bad connection,
can you swap them out for a known good unit?
and I dont play counterstrike but you might want to double check/adjust your graphics settings a little until you can get a new card,might help you a bit but not sure how much,
Hope this helps,