Viruses on a PC are a PITA, but are no reason to think you need a new PC.

OS reload, the install AVG. If there's already an Anti virus program on the comp, there can be problems with loading a new A/V program.

Load the OS from scratch, download and install windows updates, then install an A/V program. (AVG, as it is free is a good option).

Then download and install spybot S+D, and immunize the system. This blocks most adware and spyware.

Unless its a root sector virus, there's normally no need to trash a physical component of the system.