Mouse & keyboard wont work if not used for couple of hours

Hi friends,
I had to reinstall Win NT 4 server. I applied Service Pack 4 and Option Pack 4. Next, I installed MS Proxy Server 2. Finally I applied Service Pack 6a. Everything went fine. I left the server on overnight (as is the usual practice here) with the screen saver on. The following morning I found that neither mouse nor keyboard was working. However, all the LAN functions (like network printing, internet surfing, etc. from client machines) were working fine. Surprisingly, even Reset button did not work. So, I had to switch off the machine and restart it. Since then I noticed that the mouse and keyboard (and Reset button as well) do not respond if either of these is not used for couple of hours, irrespective of whether the screen saver is on or off. I have applied 'Security Rollup Package' too, but situation remains the same. Please help.

Regards.

Does NT have power options in Device Manager->keyboard that needs to be disabled?