That problem appears in 2 or 3 months, may be your hardware becomes unstable in that case you should check your hardware once every five or six weeks detaching expansion slots, clean the MB with big brush etc. Then if that problem arises then you should restrain your self to use unnecessary software and programs; even u don't use MS office regularly then u shouldn't install Ms-office at all just use portable version of this software. In a nutshell don't burden your PC with unnecessary programs. I'm using my OS for more than a year without even reinstalling it once (believe it or not its up to u). For example i use portable version of MS Office 2007 instead i use nero 8 with full installation why? 'cause i've downloaded lot stuffs from net so i've to write a lot of dvds so i need nero 8 a lot more than Ms office. So, u have to chose which software u are using a lot that should be installed. if u need a software for once or twice then use freezing softs such as Deep Freeze or similer soft to freeze ur OS or C: drive then use that soft. Or use Microsoft virtual Pc 2007 sp1 for that need.
P.S. My PC need 6 minutes to shutdown, why??? its because my XP is fully updated till date, so, it needs time to do all the stuff and shutdown all services then goes for shutdown. Now what u have to do is do a clean install (if possible download the XP professional sp3 with all update slipstream u can find it as an iso format in various online tech forum such – http://www.warez-bb.org).

You didn't mention that in your help post.
Anyways what is your PC's Configuration such as –
Processor, Motherboard, Ram, Graphics card, Hdd and etc.
Did ur PC meet the recommended configuration of Win7.
Which version of Win7 did u use?
Just detached XP parts form the earlier reply, rest are common regardless which OS u use.
Do activate ur OS through remove wat or other wares that modify system files?
Or after activating did us use Win update or update ur OS anyway?
u can think back and revise ur steps when u fresh install ur OS what happens next to 'cause such delays.

"Do u activate ur OS through remove WAT (Windows Activation Technology) or other wares that modify system files? don't got it" – এর মানে হচেছ যে আপনি কি কোন সফটওয়্যার দিয়ে কি আপনার ওস কে এ্যাকটিভেট করেন, যেটা সিস্টেমের কোর ফাইলের মধ্যে কোন চেঞ্জ ঘটায়? যদি হ্যাঁ হয় তবে ভিন্ন এ্যাকটিভেটর use kore dekte paren such as DAZ activator 2.0 for Win7.
If problem persisted then the advise would be – u should downgrade ur OS such as use XP for test purpose if the problem persists then u really need an hardware technician to look at ur hardware.

GOODLUCK