Clark is a teenager and like all teenagers hasn't quite gotten the gist about life and death. At that age, it's hard to accept. For Clark it's even harder since he has all those powers.
And teenage Clark of 1965 didn't know he could turn back time. Perhaps he didn't think he was capable of it up to his time at Metropolis. However, Lois' death pushed him over the edge, bringing back the pain of losing Pa and his impotence to stop it. In that emotional pain, he had to do something, and this pushed him past his limits (moral and physical) to turning back time.

Well, it has a nice intro sequence (could be nicer, though),
What could be 'nicer' than what is perhaps the greatest opening credits sequence in movie history?

But he COULD have "saved" him, whatever that means (we all die, it's only natural, it's not 'saving' anyone by keeping them imprisoned in an aging, failing physical body, mind you).
He had the power to TURN BACK TIME.
He could've just lived in the year 1975 all his life, and his foster parents would thus be 'eternal'. They would of course keep saying the same things, making the same jokes, and so on, but hey, at least he could've "saved him" (whatever that means, again).
This movie is contradictory and nonsensical, and that's pretty much all it is. Well, it has a nice intro sequence (could be nicer, though), and great musics. And some good atmosphere.
But it's certainly contradictory and nonsensical.

That scream is still at the same time heart breaking and chilling.
Can't stop the signal.

i don't even understand how people can say reeve's superman lacked emotion. the stricken look on his face when he realised lois was dead can still move me.
before we get started, does anyone want to get out?

It makes me sick how people are always saying Reeve's Superman was flawless and without human emotions. It's like they made up their minds before watching the movie and never paid attention.