Windows 7 - Guidance needed

Hi, I want to F disk a Windows7 hard drive, and then re-install the Windows7 Pro operating system from the DVD disk.
I am having so many problems since loading Windows 7 last July, and the feelings from one forum suggests that the problems are caused because my Grandson loaded Windows 7 over XP without first wiping the hard drive clean.
After loading the Windows 7 Pro, the hard drive was given the letter (I) and I was informed that the Windows operating system was always given the letter (C) whatever drive it is loaded on, and it should never deviate from (C) which points to an installation problem.
I have F-disk'ed an XP drive but not a Windows 7 so if anybody can provide me with the steps to take, in order etc, and in silver surfer speak (without abbreviations) I will be most grateful.
Regards Robert.

No need to fdisk it. You can simply boot from the win 7 dvd, chose custom install, advanced options< format disk. Let win 7 finish the install and that should do it.

BTW fdisk is from days gone by.

How to clean the HD Drive.
SSD / HDD : Optimize for Windows Reinstallation
Partition the Hard Drive in a Windows 7 Install
Than clean install
Clean Install Windows 7

Windows 7 was assigned the letter I because it was incorrectly run from XP and not booted for install: How to Boot your Computer from a Bootable CD or DVD

Adapt these steps to get and keep a perfect clean reinstall as it's likely something other than installing over XP has caused your performance problems: Reinstalling Windows 7

If performance problems remain after optimally installing, setting it up and maintaining it as given in the steps, then please post back the exact issues you're having for more help.

Many thanks to you all, I do not understand what went wrong with the install over XP, as you point out the DVD should have wiped the old system first before loading Windows 7, I just though that if I did it again (myself) following some correct step by step instructions, I would be starting on a level playing field.
The PC performance itself is not bad at all, although it takes a little time to boot up and shut down, even though I have my startup programs down to a minimum, it's just been one prob after the other, mainly programs that I used with XP that will not work with Windows 7, even my favourite game will not work, (so I bought another which will) and when I have more than one tab open and click a link I usually get the “ Page not available ” this prob is the most annoying, :-( so it's problems like this that I put down to a bad install of Win 7.
The main reason I wanted to start again was because I was told that the designated drive letter (I) pointed to a bad installation problem, and that got me worried.
Anyway I will first read the the info and tutorials that you have kindly posted to me before I launch into the project, and I will keep you updated as soon as I can when the OS has been re-installed.
Regards Robert.