I am not able to run ubuntu 12.04.02 in my laptop

I am not able to run ubuntu 12.04.02 in my laptop

I recently bought hp g6 pavillion 2320tx laptop with preinstalled
windows8. I installed ubuntu 12.04.02 in my lappy successfully but when i
restart my lappy it's not showing the options like windows8,ubuntu while
booting and it directly opening my windows 8.I can't able to use
ubuntu.please help me...