I would try resetting it by holding power and home for 10 seconds to see if it opens on your computer. If that doesn't work, try putting it in DFU mode or plugging it into the socket overnight. Is it detected in your Mac during DFU?
You may have rattled the internals. You might be able to take it apart and reconnect it. Sometimes it will disconnect, at least with iPhones. A cable may be loose though. You can just return it if its under warranty though, they should replace it.
I have arctic silver 5, but tuniq is cheaper and said to be much better, diamond is more expensive but it is even better. Less is more with thermal paste.