If you're performing a clean install of Windows 8, there shouldn't be any issue (providing of course that you're HDD is in good running order). If you're upgrading using Windows Vista, I'm not too sure. Some people have told me that the Windows key is registered with your Motherboard so if you change MoBo's, you will have to buy a new key (not my experience by the way).
Either way, a clean install is the best way to go so that is what I would recommend.
Make sure you have product key
Upgrading vs. Clean Installation
During an upgrade, existing user settings are retained, as well as installed applications. If you perform a clean installation, the operating system files are installed in a new folder, and you must reinstall all of your applications and reset user preferences, such as desktop and application settings.
Also there are less chances of errors in clean install
Clean install is a safe feature you see
A Windows 8 clean install involves removing the existing operating system installed on a partition (a previous Windows 8 installation, Windows XP, Linux, Windows 7... it doesn't matter) and then installing Windows 8 from scratch on that same drive. A clean install is also sometimes referred to as a"custom install."
In other words, a clean install of Windows 8 is the erase-whatever-is-there-and-install-a-new-copy-of-Windows-8 process and is usually the best method of installing Windows 8. I always suggest a clean install over upgrading, say from a previous version of Windows like Windows 7.
Before Lets get Started:
Backup Your Important Data
Locate Your Product Key
There are really three basic steps here:
Insert the Windows 8 DVD into your optical drive, or plug into a free USB port the flash drive with the Windows 8 installation files on it, and then turn on or restart the computer.
Watch for a Press any key to boot from CD or DVD... message (shown above) if you're booting from a disc, or a Press any key to boot from external device... message if you're booting from a flash drive or other USB device.
Press a key to force your computer to boot from either the Windows 8 DVD or a flash drive with the Windows 8 installation files on it.
Then do the rest yourself
Click on, or touch, Custom: Install Windows only (advanced).
Important: Even if you're upgrading from a previous version of Windows to Windows 8, I don't recommend that you upgrade. It sounds like a great option, with your files, settings, and programs all remaining in place, but the reality is often much different. You'll get better performance from Windows 8 and whatever software you choose to install again if you continue with this clean install procedure.
On the Where do you want to install Windows? screen you'll see a list of all the partitions that Windows 8 sees on the computer.
The thing that makes a Windows 8 clean install "clean" is the removal of the partition that the current operating system is installed on, as well as any auxiliary partitions that the operating system was using, usually for recovery purposes. This is what we're going to do over the next several steps.
Windows 8 Setup considers partition management an advanced task so before we can remove any partitions, you'll have to touch or click on Drive options (advanced).
Over the next few steps you'll remove the partition(s) for the operating system that you're replacing with Windows 8. Remember, it doesn't matter what operating system is currently on the computer - an old installation of Windows 7, Windows XP, etc. in ur case its win7
Now that you have access to the full range of partition management options, you can delete any partitions from your hard drive that are used by the currently installed operating system.
Important: Before you delete a partition, please know that all data on that partition will be erased forever. By all data I mean all data: the operating system itself, all installed programs, all saved documents, movies, music, etc. that might be on that drive. It's assumed that, by this point, anything you wanted to keep you've backed up elsewhere.
Highlight the partition you want to delete and then click or touch Delete.
Note: Your list of partitions may differ considerably from mine, which you can see in the screenshot above. I have one 60 GB physical hard drive on my computer that I previous had Windows 8 installed on. My primary partition, which is the C: drive when I'm logged into Windows, is 59.7 GB. That other small partition (350 MB) is a supporting partition that I also plan on deleting, which we'll get to in a few steps.
Warning: If you have multiple hard drives and/or multiple partitions on any of your drives, make sure you're deleting the correct partition(s). Many people have second hard drives or partitions that they use for backup. That's not a drive you want to be deleting.
As you can now see, all the space on my hard drive is listed as Unallocated Space. In other words, I have no partitions setup and my soon-to-begin installation of Windows 8 will be "clean" and "from scratch" on this empty drive.
Note: The number of partitions displayed and whether those partitions are unallocated portions of a hard drive, previously partitioned spaces, or previously formatted and blank partitions will depend on your specific setup and what partitions you've deleted in the last several steps.
If you're installing Windows 8 on a computer with just one physical hard drive on which you've just removed all the partitions from, your Where do you want to install Windows? screen should look like mine pictured above, aside from the fact that your drive is probably much bigger than my 60 GB example one.
Select the appropriate unallocated space to install Windows 8 onto and then click or touch Next.
Note: You do not need to manually create a new partition, nor format one, as part of the Windows 8 setup process. These two actions are completed automatically, in the background, between this step and the next.