Not enjoying my experience so far.help!

Bought a used mt3g last week. Not the 3.5 mm version. Can furnish more info  ( firmware version , etc. ) if needed but here is my problem(s)
I am using a 8gb SD card in it and sometimes it will play my music and videos. sometimes it won't.
Sometimes I have to restart it a couple of times before it will read/play what I have on my card.
The errror messages i get  are : Activity movies ( in application camera ) is not responding. Options are  force close or wait.  Neither of which do any good. For the music I get "Sorry the player does not recognize that type of audio file ".
The thing of it is that half an hour ago it worked fine . Closed that program , came back half an hour later  to use again and get the previously mentioned error messages.  Restart the phone 1, sometimes 2 times and all is well , until the next time i want to use it .

A common problem with this phone ? Something I can fix? Wasted my money on the phone ?  LOL Did i just buy someone elses headaches ?

I used this SD card in my Samsung Impression with no problems .

Anyway any help is appreciated cause I think this is a great phone  ( in theory anyway )

Thanks,
Gary

http://www.mytouch3gforum.com/mytouch-3g-how-to/mytouch-1-2v-error-'please-insert-an-sd-card-before-using-the-camera'/