What's basically happening is:
Thousands of people are killed every year in gun violence. Having a gun is more dangerous statistically than not having one, but using it or needing it are both rare.
There are cases where having one can save your life. But the gun control measures aren't about your 'right to have a gun'.
You're right, the second amendment is not anywhere close to being repealed - some would say it shouold be updated, but there's basically no chance of that.
Gun manufacturers fund the NRA, which acts as a lobbyist for their interests. They take pretty radical positions against basically any measure.
What we have now is pretty broken. It's very easy to do straw purchases for criminals, a large percent (40%?) of gun sales have no background checks.
I remember seeing a statistic I think was about 50,000 background checks that WERE done being denied, so it's easy to imagine how many sales without them happened to people who couldn't pass them, if that many people who couldn't pass it bothered to try to buy with one.
The NRA has also become a basically far right political organization, very critical of Obama; their convention last week was filled with Obama-bashing right-wing politicians.
Recent mass killings - movie theatre, Sandy Hook - have inspired new efforts to pass some measures. Joe Biden at Obama's request led a task force to recommend measures. Then a Democrat and Republican join to make a 'compromise bill'. They invited the NRA to join in forming it, and the NRA did, watering it down - and then the NRA strongly opposed that bill.
A vote was held on the watered down bill, and it got enough votes to pass a normal vote - 54 - but the Republicans basically filibuster everything to need 60, so i didn't pass.
(Really 55 - Harry Reid votes no if it's not passing for preocedural reasons).
Several Senators who voted against the bill saw their ratings drop; the Republican from New Hampshire dropped 15 points, enough to threated her re-election. Some Senators who voted for the bill saw their ratings improve. It's going to be re-introduced, advocates plan to keep fighting for it.
Most Congressional Republicans are in 'safe' Republican districts from gerrymandering, and feel vulnerable only to being 'primaried' from the right, not defeated by a Democrat.
This encourages them to vote 'to the right' to protect themselves from a primary challenger calling them 'anti gun'.
Federal Gun Control measures have rarely been passed - 1934, 1968, and 1994 (expired in 2004).
Politically, the people against the measures use a lot of straw men - claims that proponents are 'anti-gun', that they want to come and take everyone's gun, that they are violating the second amendment, and other such 'scare arguments'. Rand Paul attacked Obama for 'using the families of Sandy Hook children murdered as props'. Joe Biden described the NRA campaign as lying about the bill.
There are big regional differences on guns - people in urban areas are more pro-gun control while people in more rural areas are more anti-gun control.
The Second Amendment is very vague; it doesn't define what it means by 'arms', and for over 200 years the Supreme Court refused to say whether it included an individual right to own a gun at all. In recent years, they finally did rule on that - I think it was a 5-4 decision - where they said it is a right, but allowed regulations including background checks and bans on guns for groups where there's a reason, including released criminals.
One other topic under 'gun control' is that the Center for Disease Control has been asked in the past to do studies on what policies are effective in reducing gun violence; Republicans passed a ban on their doing any research that advocates any type of gun control; Obama has said he'd going to order more research anyway.
Another topic is that in 2006, Republicans put in a law that the Bureau of Alchol, Firearms and Explosives has to have their agency head approved by the Senate - and since then they have refused to approve anyone for the position, under Bush or Obama, trying to prevent it from functioning as much as they can.