Sounds and Video not working

[DustyDangles]

A couple days ago I thoroughly cleaned my computer and replaced the thermal compound on my cpu. Upon booting my computer up the sound does not work on anything. If I try to play a video on YouTube the video loads but does not play and if I try to play a video from my hard drive it will play but at an extremely slow rate of maybe a frame every couple of seconds.
When I cleaned my pc I had to unplug a couple of cords including the FireWire which connects to my sound system.
It is an external sound card and it shows it is connected to the computer and the computer recognizes it in playback devices and says it is connected.
This would happen occasionally in the past but i would be able to fix it by restarting my computer but that is not fixing it now.
I have no clue what is wrong, please help

So an Update is videos on the internet will now play sometimes and it shows sound is being produced when i am looking at playback devices but i still cannot hear anyting

 

[hang-the-9]

If all you did was open and put together the system, it's likely you did not connect something properly. Check your cords to the motherboard from the case. Did you test audio jacks both front and back?