[ubuntu] No other operating systems detected

I bought a refurbished Acer Aspire 5 laptop with windows 5 installed on it, and I tried installing Ubuntu 13.04 amd64 by booting from my pendrive alongside windows 8. When I got to the third screen, it told me that there was no other operating system detected, and didn't give me the option of installing Ubuntu alongside windows. I didn't understand the other posts about how to fix this problem.

Please help!