Disk boot failure after trying to replace soundcard.

Hi, so i was trying to change my sound card, but the new sound card wasn't compatible with my computer. So i went ahead and put my old sound card back in, screwed everything back on. turned on my computer, and next thing i know it says, "disk boot failure, insert system disk and press enter". All i did was try to change the sound card. I don't think i unplugged anything else or moved anything around. I made sure everything was in securely too. I have no idea what to do now.