[quote name='Kain Vincent']1. Check the screen for any dead pixels.
2. Make sure the buttons are working fine (the 1000 model has a poor d-pad).
3. Make sure the UMD drive or memory stick slot are all in order.[/QUOTE]
Everything I was going to say, however I will elaborate further (hopefully helping a bit more).
[quote name='Kain Vincent']1. Check the screen for any dead pixels.[/QUOTE]
I'd also check for scratches (which might at first seem obvious but still majorly essential, I absolutely hate scratches).
[quote name='Kain Vincent']2. Make sure the buttons are working fine (the 1000 model has a poor d-pad).[/QUOTE]
You shouldn't have to apply too much pressure to the buttons to get them to work, so press like you would normally with medium pressure. If you are required to push harder than usual it can be a big annoyance. Also, press down the d pad on all buttons and listen for a squeak. If it squeaks, it doesn't mean it's broken or anything, it's just really really annoying. :lol:
[quote name='Kain Vincent']3. Make sure the UMD drive or memory stick slot are all in order.[/QUOTE]
This part is absolutely required. 1000's have a switch to open and close the UMD part so check that is all in order (although I've never heard anything go wrong before), newer models are just opened manually. Also check that it will actually read a UMD, otherwise it's rather pointless.
Hope I helped!