Freezing Problem HELP!

HELP

basically if i talk on the phone, or surf the net, or run anything for longer than 5 minutes, my phone will freeze.
Afterwards the phone wont startup for a very long time. It will keep freezing starting up. it freezes about 5 to 6 more times before the phone fully loads.

I didn't download anything to my phone in fact I barely used it.
I bought my phone overseas

any suggestions on what I should do?
should i perform a soft reset or perhaps a hard reset.

i cant even charge my phone without having it freeze after 5 minutes    

could this possible be a overheating problem? because there were times that instead of freezing, it automatically restarts then freezes once it restarts.