iP4 Picky about what PC to sync with

[SL4VE]

my iPhone crashed day before yesterday and been trying to restore it with my PC all night with no joy. Restores halfway and than crashes. tried this about 5 times with no luck. Than read on another forum to try a different machine. So i tried my sisters PC same WIN7 etc same iTunes version and WOW it restored perfectly. Now my iPhone syncs to my PC but wont restore at all to my PC. How the hell do i fix this, i have already re-installed iTunes to no luck

Also when i sync'd with my pc it didnt synce the apps so just restored again to see if it will, really pissing me off now had to go all day yesterday without a phone too

Thanks in advance

P.S just restored back to 4.2.1 on custom firmware as i know it run's stable

 

[SL4VE]

finally restored it and now it wont sync with my itunes. restored via sisters laptop. what dramas off to apple store to break something