Prime will punch sentry so hard he destroys him to the molecular level.
Prime will punch sentry so hard he will send him several dimensions away or to a different timeline. lets see him reforming in 1000 B.C
Prime will destroy sentry with his heat vision and keep melting him preventing him from restoring himself at the very least enough for a KO.
Just to clear something up, because so far this battle is very one-sided, while it actually shouldn't it.
In my opinion there is no way Superboy-Prime can win this fight. Why not you ask?
We all know that Superboy-Prime is an EXTREMELY emotional character and that is understandable, because he went through a lot in his life: He saw his family and friends die, he wanted to be a hero but was misunderstood and killed others, he finally went bonkers and had to fight everyone, got abused by the writers, lost his girlfriend and so on.
On top of that he doesn't really have an immunity to telepathy, or better yet empathy.
Sentry would easily be able to win the fight by mind-raping Superboy-Prime.
Sentry has telepathy, which exceeds the planetary level, because not only did he erase the memories from everyone on the Earth including characters like Doctor Doom, Hulk, Thor and few Omega Level mutants, who are all very resistant to telepathy ... no, he also erased the memories from the Inhumans on the Moon.
As the Sentry he calmbed down an enraged Savage Hulk in a matter of seconds, he mind-raped the Super Adaptoid by showing her the Void and as the Void he mind-raped so many people by showing them their miserable past, presence and future.
Superboy-Prime had to go through so much crap and facing an intensified version of that would send him into a shock state and end the battle quickly.