At last I bought Windows 7 ultimate for $320 ($2,499), from history here I bought Vista nearly 3 years ago. The rearm trick didn't work and I have no other alternatives of OS for work. My MacBook Pro just can't connect to network resources running obsolete versions of windows server here.
To do that first of all I need elevated privilege as administrator, do that from below
then I ran this slmgr - rearm, I then got a successful prompt and rebooted it.
Windows is still shutting itself down every 2 hours?
How much longer I can use my Evaluation copy? Type "slmgr.vbs -dlv" in cmd.exe you'll find out below.
You may get a different expiry date if you run 'winver' in command line since you are allowed to extend the evaluation period a few times, that's called 'rearm count' or Re-Arm a grace period of 30 days each count.
Other tricks I may need to extend the life of my RC copy are here and there.