How can I tell when Windows NT was last started?

A. From the command prompt, enter the command

C:> net statistics workstation | more

At the top of the display, you’ll see statistics since.... This statement gives the time since the workstation service was started. The uptime will be incorrect if someone has performed the commands:

net stop workstation
net start workstation

The PVIEW utility also displays the time that Windows NT has been running. A set of applications called 3UPTIMES.ZIP displays this information. The set includes a command-line and a Windows version. You can find information about these applications from http://barnyard.syr.edu/~vefatica/.Be aware that this utility gives incorrect information if the system has been running more than 50 days.

The last line of output from the Windows NT Server Resource Kit utility srvinfo.exe displays the total uptime in the format:

System Up Time: 24 Hr 3 Min 29 Sec

A performance monitor object is available from the Performance Monitor tool (perfmon.exe).
Object: System
Counter : System Up time

ElWiz from http://www.heysoft.de/nt/eventlog/ep-elwiz.htmwill always give you the correct uptime (along with other useful information and is free.

System Internals also provides an uptime utility. Visit http://www.sysinternals.com/misc.htm for information about the utility.