SQL Server can experience corruption; one time we had a corrupt record - a TEXT field from memory- and any query that strayed in there locked with SQL Server laboring mightily over some pointless task.
From memory, we found it by doing a row-by-row manual backup; it stopped at the culprit row, which we deleted.
Regards
j.R
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1
