Windows crashes automatically if you don't switch off  the machine for
49.7 days.This is accepted by  Microsoft.

Do you know why?

In windows the Virtual Machine Manager(VMM) is  responsible for
creation, exe cution, monitoring and  termination of virtual machines. This
VMM is a
32 bit protected mode operating system, provides a  number of system
service at chip level of programming.

One of these services is "Get_System_Time". This  particular service
loads the EAX register with the  time in milliseconds since Windows
started.This service is accurate to 1ms.

EAX is a 32 bit register. So the maximum number of  milliseconds it can
hold is:

(2^32) - 1 = 4294967295 milliseconds
= 4294967.295 seconds
= 71582.79 minutes
= 1193 hours
= 49.7 days

So after 49.7 days the EAX resets to zero.Most of the  Drivers use this
Time Service to keep track of the   time out of various services they
provide. So after  49.7 days the drives cannot use the Get_System_Time
funtion of VMM and they crash.

"SO DO NOT KEEP YOUR MACHINE ON FOR MORE THAN 49.7  DAYS. IT WILL NOT
ONLY CRASH BUT M AKE A BIG HOLE IN  THE POCKET(THE ELECTRIICTY BILL)