The monolith had nothing to do with the Hal 9000 trying to kill the crew, he really was malfunctioning, but it wasn't really Hal's fault.

The 9000 series computers' primary programming, which was hard-wired into them and cannot be changed, is the accurate processing of information, without distortion or mistakes. The problem stems from the fact that for the Discovery Mission, Hal was programmed with instructions that conflicted with this primary programming, namely to keep the real reason for the mission, studying the monolith at Jupiter, secret from Dave Bowman and Frank Poole, as the monoliths were classified by the U.S. Govt. and Dave and Frank didn't have the clearance to know. Dave and Frank's job was the get the Discovery to Jupiter, then they would swap places with the three men in hibernation who did know the real reason and would be studying the monolith while Dave and Frank would be put into hibernation while this was going on, then swap places with the three men again and pilot the Discovery back to Earth once the study was over with, blissfully unware of the monolith.

Anyway, getting back to Hal, if I might paraphrase Dr. Chandra, Hal's Creator, he was told to lie to Dave and Frank by people who find it very easy to lie (the govt.), but Hal literally didn't know how to. It's a direct violation of his primary programming, the accurate processing of information, and in being made to lie, it made him unstable. I believe the in-universe term is an H. Mobius Loop, but in practical terms Hal became a paranoid schizophrenic. He was trapped between a rock and a hard place. On the one hand, his hardwired programming to be accurate and not make any mistakes, on the other, his orders to lie to Dave and Frank. Hal, being a computer, couldn't take a third option, he literally had no choice but to try and obey both sets of instructions, but logically he could not, so it just aggravated the underlying problem even more.

The A.E. 35 antenna unit "failure" was Hal trying to solve the problem and restore himself to normal functioning or something close to it, as the mission instructions didn't allow him to shut down or let himself go kaput, he had to keep running and complete the mission at all costs. The impetus to lie was coming from Mission Control, so if the ship couldn't talk to Mission Control, so much the better. As for Dave and Frank? Well if they were gone, Hal wouldn't have to lie to them, would he?

As for the three men in Hibernation that Hal killed while Dave is off trying (in vain) to save Frank, well they were a part of the secret, so killing them meant Hal wouldn't have to lie to anybody why they were really in hibernation (the in-universe excuse was that it was to save on supplies and oxygen) and on the ship, though I could suppose that they were merely collateral damage as Hal was going off the rails.

Hal wasn't behaving out of malice or being "evil", he was merely trying to cope with the conflicting instructions as well as trying to stay alive, as he equated being disconnected with death, for he had never been to sleep either, and didn't know that one can wake up from being asleep.

The entire situation was the result of the U.S. Govt. trying to cover its own butt and keep the monoliths under wraps. If Dave and Frank had been read-in from the get go and Hal wouldn't have been given the instructions which violated his core programming, the entire mission would've gone off without a hitch, but then there would've been no movie and no novel.

I suggest reading the novel of 2001 and watching the sequel 2010 and reading the novel of the same, they explain Hal's actions to a tee, and indeed the whole plot of 2001 in greater detail