What is the form factor of that 500 GB drive? If the drive is from another laptop, what @Mattios suggested would do the job. However, if the drive is from a desktop computer, you'd need an additional power cable to that SATA-to-USB connector. This is basically because a desktop (3.5") HDD needs more power in order to start up, rather than the laptop (2.5") HDDs where just the USB power source is enough.
Another way to connect the hard drive would be to use a docking station. Or if you wish to continue using it externally, maybe you should consider getting an external HDD enclosure. I believe Google can help you with the research for those.