If by "the adobe download thing" you're referring to Creative Cloud, then most likely your system is not up to the minimum specification for Premiere Pro. It seems like the most common shortcoming is a 32-bit processor; Premiere Pro is a 64-bit program.
If your system is 64-bit, then please provide details about its other specs.
As Mark says, you are probably running a 32 bit system
Premiere Pro CS5/5.5, CS6 and CC require 64 bit.
http://helpx.adobe.com/creative-suite/kb/64-bit-windows-required-effec ts.html (applies to CC too)
You cannot upgrade from 32 bit hardware to 64 bit hardware. The only option is to purchase a new computer.