Windows - No Disk

[nin137]

This error pops up randomly despite anything that i'm doing. I don't know where it came from or why it is prompting me to put my windows xp disc into the cd-rom drive.
has anyone else experienced this problem? i just click continue with the disc in and it is ok, but it is very annoying, any help is appreciated. (i had a start-up problem yesterday, i posted this in the security forum). thanks!