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In February 2001, it was announced that the band had covered the song "Midlife Crisis" for a Faith No More tribute album, however the cover was not used. On June 4, 2002, Disturbed released a documentary DVD about the band, titled M.O.L., which showed some of the band's more personal moments in the studio and during tours, as well as featuring several music videos and live performances.

On September 17, 2002, Disturbed released their second studio album, titled Believe, which debuted at number-one on the Billboard 200. The music video for the first single from the album, titled "Prayer", was pulled from most television stations, due to the similarities it had with the September 11, 2001 attacks. David Draiman recorded vocals for a song titled "Forsaken", a song written and produced by Jonathan Davis of the band Korn, released on Queen of the Damned.

During the Believe record cycle, Mike Wengren mentioned on Decade of Disturbed that he couldn't remember much of this time, that it was a darker time for him and that he used alcohol as a coping skill.

This was mainly due to his mother battling cancer, the tension between him and the rest of the band, and his fiancée at the time leaving him. He also stated that he would use his "Mikey Chronicles", which were of him acting comedic, to numb the problems.

In 2003, the band once again participated in the Ozzfest tour and started another one of their own tours, titled Music as a Weapon II. The bands Chevelle, Taproot, and Unloco toured with them. During the tour, Disturbed debuted an unreleased song, titled "Dehumanized". After Disturbed finished the Music as a Weapon II tour, Steve Kmak was fired by the band because of "personality differences".

He was replaced by John Moyer, who is now the current bass player. On the night Moyer became the band's new bass player, Disturbed played live at the House of Blues and performed two new songs, "Hell" and "Monster", both of which are B-side tracks on the band's third studio album, Ten Thousand Fists.