This sounds like a no POST situation/ Do you have any LEDs lighting up (e.g. ASUS mobo will light up the hard disk activity LED solid if there is a problem with it trying to POST).
Check out the recovery guide:
10 Step "No Post" BIOS Recovery Guide
From your description, you said the problem started when you tried out the sound and wireless card. Either something is odd with those two cards and / or their slots, or you disturbed something else within your computer.
Check ALL connections (e.g. did you pull out or dislodge the CPU power connector when you were installing the other cards) - if you find something wrong, fix the connection and try to POST again.
If that doesn't work, remove the wireless and sound cards and see if the computer POSTs.