Hard drive spins madly?

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FORMATTING
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When you had re-installed Windows Vista, you had formatted your local system drive (which is your C drive). Formatting your HDD will erase everything on it, which is why you cannot format the partition from which you were running your system. If you have another partition on your HDD, you will be able to format that, like you would format a USB Flash Drive.

Here is a nice tutorial on how to format your HDD: http://www.youtube.com/watch?v=mME9VLT7-xw It's showing you how to format your HDD when installing Windows 7, but the process is exactly the same in Windows Vista.

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BUSY HARD DRIVE
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Here are several reasons why a HDD may be really busy:
(1) You have not defragmented your HDD in a while. You can rule this out since you re-installed Winodws Vista.

(2) Your HDD is full. If more than 50% of your HDD is used up, move your files that you don't use to an external HDD. I don't think this is the problem in your case.

(3) Your HDD is reaching its end. This could be the problem in your case. I suggest that your run "disk check" and see if you have any bad sectors on your HDD. In any case, you should backup your documents, music, videos and pictures onto an external HDD if your HDD stops working.

(4) Viruses could be doing things in the background and keeping your HDD very busy. But, you can rule this out since you formattend your system.

(5) Not enough RAM. "troubled31701" above is absolutely correct. You may not have enough RAM, so your system is using your HDD as "virtual memory". For Windows Vista, you need to have at least 2GB of memory; 4GB would be great.

Your HDD will always spin as long as your computer is on, but the "hard drive activity light" should not be blinking all the time when you are not doing anything on your computer. You can set your HDD to turn off if your computer is not in use for a certain amount of time. But, as soon as you move your mouse or hit a key on your keyboard, it'll start spinning again. This feature is mainly to save power, but it'll also keep your HDD cool. You can change the setting in "Power Options" in Control Panel.

The Hard drive always spins while the laptop is on...that is the way in which it was designed...

Chances are you hard drive being accessed all the time is due to inadequate System Memory forcing the hard drive to be used a virtual memory...

Answer 1:
Yes, their could be some backdoor virus running though your system
Solution: try installing Norton Antivirus(recommended) and do a full system scan

Answer 2:
Try to boot your windows OS(win XP/Vista/7) and as you go through the installation process you could format the C: drive.

Answer 3:
most probably your
(a) Pc might have fall or bump it on a hard surface that makes internal chips especially the hard disk to lose or make some files gone "corrupted"(check if you experince).

(b) you might have overloaded your hard disk space with less than 30% of its whole(try to do backing up/deleting files that are not relevant for this time)

(c)old hard disk really has its own lifespan especially if its being used everyday without checking its temperature, space(its GB),viruses, etc.