Actually sometimes vendors of motherboards (mostly notebook ones - a 2430M seems to be a notebook processor, so I can assume that you have a notebook) lock this option - hide it from the BIOS menu. There could be three ways to enable it - first one there MAY be an utility from the notebook or motherboard vendor which could enable or disable it. Second one - you can try to upgrade the BIOS of your computer from the vendor site - it MAY happen that they reenabled that option in the BIOS menu. Or you will need to "hack" your BIOS - or ask people who know how to do - but this is high risk.
Also, that may be that the VT-X option is called differently in the BIOS menu - try to enable some things like "Virtualization" and similar, but be careful!
PS: Reinstalling an OS won't help at all. The OS doesn't manage this option - the only thing it can do is supporting or not supporting it. But Windows 7 supports it, so this is not an OS issue.