ATV 2 wont switch on

Have had no problems with the ATV2 since purchasing. It was already jailbroken with season pass and i have never updated firmware or anything. Until yesterday when i did an update all on Nito tv(i think), since this was done the ATV2 will not switch on when the internet is on. It loads apple logo, stays on for about 30 seconds then goes to a circle ( loading symbol?), then it switches off. It keeps repeating the process (minus the apple logo). I urgently need help as i was selling it on and now I  may be losing out on the money and have a duff atv 2 on top. It is on firmware 5.0.2. I really want to avoid doing a restore and then having to jailbreak it myself,as i have no experience of that what so ever. PLease help