Sorry I couldn't do a quick search and I'm using my iPhone. If Captain America from Hammer of Thor is in melee, can he still make a range attack against someone else? Thanks!

No, he may not. When making a ranged attack his LoF is only blocked by walls and indoor blocking terrain. But all other rules pertaining to ranged combat attacks act normally.

And the rule in question is that characters cannot target other characters with a ranged combat attack when they are adjacent to opposing characters. I'd quote the Rule Book, but I'm currently firewalled.

Even if Cap was a sharpshooter, he would only be able to target the opponent adjacent to him.

Wow so sharpshooters wouldn't be able to target other opposing characters from range if he is adjacent to another opposing character? I did not know that. I guess I've been playing wrong with sharpshooters.

Nothing in the Sharpshooter ability description indicates that they can, so they can't.

And since people do ask questions about this (understandable), there's this bit from the Player's Guide that spells it out:

This ability allows the character to make a ranged combat action/attack while based. If the attack targets, then targets of the attack must be the adjacent character(s).Regardless of targets, non-adjacent characters can be affected by the attack (such as would be the case with powers like Pulse Wave and Energy Explosion).

And here is the text rowdyoctopus is referencing.

From p. 10 of the 2010 Core Rulebook: