getting new PC

ok i got some info from my dad and he said he getting me a pc for graduating but only going to pay $500-$600 but lol i could get him to get as far 700 so my question is which one should i get that is more suted for gaming and multi tasking and that comes with every thing like the moniter and speakers and all that good stuff. the manufacture to matter i dont thank tho all the computers he buys now are from dell so he may just choose them ne way but ne recimendations from you guys/gals is very much apreceatied. -thank-

ps im on my dads pc atm and i some how changed the back ground from a pic i was looking at online and it got set to it and i was woundering how i get it back to wut he had cuz what he had is not on the list in the propertie thingy

 

nvm the secound question i found it in the computer and got it set back to it