I continue in the Sudden Strike thread to not derail this thread totally ;)

By the way, 'traduction' = 'translation' in English and the verb is 'to translate'.

Oups, thanks for correcting me ! That's a huge mistake I was used to do XD

So, before going on holidays, I thought it could be nice to gather as many software as possible who were suggested along this thread into one post, just in case it could be useful to someone one day.
So, here is a list of them (there may miss some though ;)) :

Ubuntu/Linux Live USB :
Ubuntu Live USB Tutorial : Suggested here (be aware of potential issues with EFI, USB2 and FAT32 !)

Clone your old drive :
: ease the pain of the drive if your files were fragmented. Suggested [url=https://www.gog.com/forum/general/my_computer_need_help/post15]here (and more explanations here)

Try to retrieve data :
: Suggested [url=https://www.gog.com/forum/general/my_computer_need_help/post13]here.

Erase properly :
: a zero-fill tool. Suggested [url=https://www.gog.com/forum/general/my_computer_need_help/post10]here.

How to install Windows 7 from scratch (and find a Win7 image) :
How to Do a Clean Installation with Windows 7 : talked about it here.

Find & update your drivers :
: suggested [url=https://www.gog.com/forum/general/my_computer_need_help/post33]here.
Snappy Driver Installer : suggested here.
DriverPack Solution : suggested here.
How to do it manually : How to... suggested/some explanations & [url=https://www.gog.com/forum/general/my_computer_need_help/post87]here.

Anitivrus & Anti-malware :
Malwarebytes anti-malware
AdwCleaner
Kasepersky Free Version (yes there is a free version)

Get infos about your specs/comp' :
: suggested [url=https://www.gog.com/forum/general/my_computer_need_help/post30]here.
: suggested [url=https://www.gog.com/forum/general/my_computer_need_help/post30]here.
And specifically about your disks :
: suggested [url=https://www.gog.com/forum/general/my_computer_need_help/post69]here.
: suggested [url=https://www.gog.com/forum/general/my_computer_need_help/post71]here.

Checksum your files :
HashCheck Shell Extension : suggested here.
dvdsig and rhash : suggested here.

File manager :
Total Commander : suggested here.

Copy files faster and more securely :
[url=http://www.codesector.com/teracopy]TeraCopy[/url] : suggested here

And finally, these are very useful (at least for me) :
Ccleaner
Defraggler
Pale Moon : replace Firefox :D (and I strongly recommend to take a look at Adalia Fundamentals & Barefoot Essential for an infinitely better experience when using GOG website)
f.lux : reduce eyes tireness when working on comp' at night
DesktopOK_x64 : If like me you have [a lot of] icons on you desktop, but sometimes some softwares/games mess your organization a bit because of resolution switchs for example : this enables to quickly save the layout of icons whenever you want, and restore it when you want. VERY handy.
FreeFileSync : Synchronize Files and Folders, & can check if what's in two folders is the same.

And some other softwares suggested here !

[Oh, and if you have issues with "Windows Games Explorer" in Win7, take a look here ;)]

--------------------------------------

I'll maybe update later :)
Just in case : does anyone know an efficient way to not have too much icons in the desktop and still have a very quick way to launch softwares ?(yeah, I find start menu of windows not very handy to launch things).

Again, a huge thanks to everyone who were kind & helped me ! :D

Maybe put some icons in folders on your desktop? I have my games' shortcuts in such a folder.
Or try these little tools: Qsel and PopSel. I haven't used them, but I use TTclock from the same developer.

http://www.horstmuc.de/wqsel.htm
http://www.horstmuc.de/wpop.htm

Edit:
Links not working properly.

I create a quick launch bar to the right of taskbar (I'm basically right-handed) with subcategories in it, one of which is "Games". Keeps the desktop clean, provides easy and quick access with a single click, it's easy to do, and doesn't require any extra software.

I could walk you through it, if you're interested.

There is also that one they use in OSX and also KDE version of Linux Mint comes with that as standard. (I always turned it off though... but it works well enough.) That launcher bar or whatever it is called.

^ Simply this

Btw, I also created subfolders categories in the start menu.
I don't know why so many people never think about such possibility..