There comes a point in the life of every office computer when it is simply no longer practical to keep it running and up-to-date. When it comes time to get rid of old, outdated computers, it's not enough to simply unplug them and toss them in the nearest trash can. Disposing of old PCs requires you to do several things first, partly to appease environmental safety regulations, and partly to protect your business.
The first thing you will want to do before getting rid of an old computer is to completely backup everything on the hard drive. Often, it's simpler to just make a full disk image rather than backing up individual files. A disk image is an exact copy of your hard drive that acts as a sort of virtual drive that can be mounted or recreated just like a physical drive. This will allow you to keep all your settings, files, and configurations intact in case you ever need them again. It will also make the process of recovering old files simple, since once mounted, the disk image will essentially perfectly recreate the state of the computer when the image was made.
Once a backup is performed, you need to inventory any software that was installed on that computer. While most of it will likely be easily replaceable or out of date (hence the need for a new computer), you might find a piece of software that you had forgotten to move over to the new machine. Make sure you pay attention to any configuration options, and if you can, export these configuration profiles to the new replacement computer to make switching over simple. Also, check for any software or product keys that you might need to copy to activate that software on the replacement computer.
Finally, have someone from your IT team remove the hard drive. Completely erasing the data from a hard drive is difficult, if not impossible under most normal circumstances, and you don't want to risk your company's proprietary data falling into the hands of hackers or competitors. Once the drive is out, you can either put it in storage, or physically destroy it to make sure that none of the data on it gets stolen. Remember, simply doing a hard drive wipe, format, or OS reinstall is not enough to keep your information secure.
Once these steps are done, you can take your computer to a recycling facility, give it away to a charity, or dispose of it however you see fit.