How many time/computer I can install Windows 7 ultimate per license to be activate?

I have recently purchased a new license copy of Windows 7 Ultimate edition and installed it on my Sony Vaio desktop computer. Everything went as expected and it is up and running with out any problem. I then thought of to install the same Windows edition on my fathers laptop but even after successful installation, it is still asking me for the activation key. I had tried using the same key which I am using on my computer but the laptop is not accepting the key.

So this raised a lot of questions in my mind. Like on how many computers can I use this same product key; how many times I can install Windows 7 and use the same activation key. Moreover, if I upgrade my computer with new hardware including motherboard, hard drive etc then is it like I have to purchase a new serial key for activation?

No matter from where you purchased that license and also which version of OS you are using, however you can install Windows 7 only on one machine per license. So if you want to install it on some other computer, you may use the same Windows installation CD but need to purchase a separate Windows 7 license for activation on each computer. To just get the license, contact Microsoft support team. It should be cheaper to cost.

So if I need to install it on my fathers computer then I have to ask MS for new license key? But as I have heard from many people that you can use the same license for at most 3 computer. And if I am not wrong it was related to Windows XP edition. So why this is not repeated in Windows 7?

Basically this is kept so to avoid piracy and the license about which you are talking should be a special Family Pack. In Family Pack license, you are allowed to use the same license for up to 3 computers. This licensing scheme was also in Windows XP and the same has been continued in Windows 7 also. So don't be in the impression that something have been changed in Windows 7. It is not the case.

And what about if I upgrade my hardware on the same computer, do I have to get a new license once again and pay MS for new license? It would be irritating and costly for me to pay the company just because of I am upgrading my system. Isn't it!

Basically a license is activated based on your OS and computer hardware details. So if you make any major changes in your computer then I suppose you may contact Microsoft explaining the things. Ideally, they should provide you with a new activation key or allow you to use the same key. But there is no solid words to it and so can't help you much on it.

You can install it at least 3 times. Disconnect your computer from the internet before installing. Use the call feature for activation, NOT internet activation.
If Microsoft really meant for single licenses at $200 a pop, they would lose many many customers...but they understand the competitive nature of this business and leave intentional loop holes. Look at OSX, no license, even for a better OS than MS. They even sell OS's for $15-$30 (Snow Leopard).

Soon, the world will turn to MAC's. Catch the wave buddy!

ONE time of course. Why would you think you can install on as many machines as possible?

The only exception is the VLK release for corporate users.

I'm sure most people here have stolen their Windows install -so they can install as many times as they want.

Don't be a thief

^ most people spend so much money on harware, they dont spend a little more on getting real windows.