I think Sylar stopped Hiro one of 2 ways
-he can 'Freeze' time
-Hiro got weak because he couldn't kill-so it it was his weakness that lost his power-not Sylar's doing at all.
I DO like John's theory for the virus on Sylar- wonder if the show producer's thought of that one though
I think the sword his dad has is a better unbreakable one and his dad will make Hiro into a fearless warrior too.
I think explanation #2 is correct. Sylar has no power over time - if he did, he would just freeze time when killing his victims or at least stop anyone from running away. Makes more sense that Hiro lost control - he has admitted that he doesn't really have much control over his powers.
Personally, I can't wait for Sylar to get his due. They've done a great job of making him the guy to hate. I'm worried about him becomming too powerful at this point. I'm still not sure about who's going to explode, if anyone. I'll be surprised if its Ted - he seems to be gaining so much more control over his power. I still don't get what Linderman and company hope to gain out of killing off a million people. They could easily expose that people have powers if they wanted to and they'll have Nathan in the president's office, so what more do they want?
Here's a big Spoiler guess for you.......................................I think Linderman is going to use Micah to control the voting results for the election, which is how Nathan gets elected despite being so far behind in the polls.