Vov System Uptime is a free utility that silently records your system's uptime and allows the details to be quickly displayed.

Not a complex tool but it will give an accurate count of exactly how long your machine has been running and since Windows makes it difficult to obtain this data this tool provides a simple alternative.

Vov System Uptime resides in the systray, and all it does is count the time. There is an option to copy the current uptime count to the clipboard for record keeping on a particular machine.