My cydia icon has gone, how can i get it back?

I was deleting themes and tweaks off cydia and it said to respring so i did, then it wasn't there anymore. Iv tried restarting it and turning it on and off a number of times but its just not there. I still have the theme and tweaks i had on before it had gone but now its just not there. Help! I have a iPhone 4s btw!

Added (1). Pressing the home button and the power button do not work.

Hold the "home" button and the power button together, let it turn off, keep holding until you see the apple logo, then let go, hope that works for you.

Added* Re-jailbreak your phone, use http://evasi0n.com/ to download the appropriate software for your device, connect your iPhone and run the software and follow the on screen instructions. (this way your simply refreshing the jailbreak).