I was never very good with interrupts, so I dont know how to tell you to check this, but one possibility is interrupt conflict between parallel ports, serial ports, sound card, mouse, and cd. Another might be drivers. It seems to me like interrupt 5 is one that sound blaster likes to use and that sometimes you had to pull the parallel card and rejumper it to a different interrupt (7 maybe?).
My first cd rom / sound card kit came with a lot of very complicated instructions for setting card jumpers, autoexec bat entries and so on. I finally had to give up and take it into the shop, when I got it back, they told me I'd gotten the settings worked out ok, but didnt have a current enough mouse driver.