I suspect your CPU doesn't support the VT-x feature, as others have stated. As Joshua pointed out, the Intel website will help you determine the capabilities of your CPU. Specifically you should check the Ordering/Spec page, since different revisions of the same processor may have different features.
Basically if your E5300 isn't the SLGTL Spec, then it doesn't support VT-x. The only way to be sure is to find out your Spec Code, either from the box it was packaged in or physically looking at the CPU. You can also try programs such as CPU-Z or Intel® Processor Identification Utility which will tell you if VT-x is available, but I think only if the option is enabled in BIOS.
Updating your BIOS wouldn't necessarily solve the problem either, because the CPU would still have to have the VT-x feature. Now if you update your BIOS, and there is still no option available for enabling VT-x or hardware virtualization under the CPU settings, then most likely your CPU doesn't support the feature.