How can I reload the android OS?

Thanks for your help!

Its imperative I fix this, kids are going away and need a phone.

When I turn on the phone (Samsung Galaxy S II) which is a trac phone. The only thing that happens is the Start up logo (S G II) displays in white lettering like it normally does when you turn it on, but then it just keeps reloading the same logo until the battery dies.

When I hold the volume down and power it on it does go into the recovery but only allows me to restart the phone. Which will keep displaying the samsung logo over and over until the battery dies. When I try hard resetting it acts like its working but wont connect??

Just says Connecting with the green android .