Just about everyone assumed Megadeth frontman Dave Mustaine's musical career was over after he fell off the wagon and suffered a nerve injury in 2002 that left his left arm completely numb for four months. Even Mustaine had doubts about whether he'd be able to perform again.

The accident took place in rehab, when Mustaine fell asleep with his arm draped over a chair and seriously compressed a nerve in his left bicep (see "Megadeth Pack It In After Nearly 20 Years"). Doctors told him he might never regain full use of the arm, let alone play guitar. So the metal icon broke up Megadeth and went into hibernation for the rest of the year with no real plans. He even offered bassist David Ellefson rights to the band's name. But something inside him refused to give up.

"I had this fire in my belly I thought would go out when I finally retired," he said a few weeks prior to the Tuesday release of Megadeth's new The System Has Failed. "I guess I wasn't ready to quit because it didn't go out."

Once Mustaine regained some feeling in his arm, he began an intensive year-long weight-therapy regimen. Every day he'd go to the gym and lift with the hopes of regaining enough strength to eventually pick up a guitar. "My left arm had completely withered, so I was lifting these two-pound dumbbells," he said. "You know what color those weights are? They're pink. So I'm in the gym, and these meatheads with horse jaws are looking at me, and I'm going, 'Dude, don't even say it.' "

After regaining strength in his hand, Mustaine still needed to work on his dexterity. He hired a guitar teacher, labored over scales and other exercises, and in the process learned a bit about music theory. "I was a totally self-taught guitarist, so I said to my teacher, 'OK, let's start at the beginning.' The guy was like, 'You've gotta be kidding,' and I said, 'No. I know what I'm doing, I just don't know what it is that I'm doing.' "

Last summer, when Mustaine regained full speed, he started writing songs for what he thought would be his first solo album. Record label EMI, however, told him a solo disc wouldn't fulfill Megadeth's contract promising them one more album. So Mustaine decided to record a Megadeth disc, though none of his former bandmates was willing or able to be involved. "A lot of people say Dave on his own isn't Megadeth," Mustaine snarled. "The bottom line is: There's nobody left in the band but me, and the album still sounds like Megadeth."

The System Has Failed doesn't just sound like Megadeth, it sounds like vintage Megadeth and is Mustaine's heaviest album since 1992's melodically thrashing Countdown to Extinction. The disc features plenty of crunching speed riffs and sneering vocals. The songs are catchy, but the abrupt rhythm changes and fiery guitar solos maintain a propulsive feel throughout. And while the band's last few albums have featured polished production, overt radio hooks, and modern rock flourishes, The System Has Failed sounds genuinely dangerous from start to finish.

"Megadeth really lost its way after Countdown to Extinction," Mustaine admitted. "That was when Nirvana came out with Nevermind and lots of things changed. The band kind of lost its identity, started to pursue other outlets, and tried to be successful instead of staying true to itself. This time I wanted to make a real metal record — something liberating for me without worrying about radio play or sales. And there were no holds barred."

In the process of revisiting classic Megadeth sounds from albums like 1986's Peace Sells ... But Who's Buying? and 1990's Rust in Peace, Mustaine recruited original guitarist Chris Poland to record solos for many tracks on the record. The reunion happened last year while Mustaine remixed tracks for the re-release of the Megadeth catalog. After working on the band's first disc, Killing Is My Business ... and Business Is Good!, he invited Poland to the studio to hear the mixes. Following a bit of reminiscing, he decided to invite the guitarist to guest on the new album.

The move surprised Poland, who had been fired from the band in 1987. It's even more surprising considering the physical confrontations that once went down between the two.

"I beat the hell out of Chris after gigs so many times, but he never felt it. It never dawned on me that the guy wasn't feeling it because he was on heroin," Mustaine recalled of his ex-bandmate, who entered rehab after leaving Megadeth. "I'd punch him until my hand was bashed in. Then we'd wake up the next morning, hug each other, and move on. That's the kind of relationship we had."