How should I get rid of the plugins and samples on my old computer as it won’t be used for music anymore?
Should I desactivate and uninstall each plugin or sample library according to some specific procedure related to each individual developer? Or can I simply reset the entire computer without worrying about losing activations and the like?
The horror!

I would look at each and then decide. I don't think I have any old authorization schemes that need to be deactivated from the computer itself. Most will allow me to deactivate a computer from the website. But there is still those (talking to you Waves) that use that type.

Thanks Grem!
Wonder if there’s a forum thread somewhere about this.

You should look at them as Grem suggested.  Especially iLok stuff, make sure you deactivate first.

Once you've squared away any authorization/activations issues, you can reinstall Windows... or a backup that's just a clean install of Windows.

If you use the soft iLok for anything, definitely deactivate those products!  Have heard that if you brick or wipe the computer, you will have to go to each developer to recover any activation for that device.
 
You will probably burn an activation for any IKM products installed, but since you get like 10 activations for each product,that shouldn't be an issue.
 
I think that activations from NI, Celemony/Melodyne, or XLN can be managed from your online account.
 
I am new to Waves, so I am not sure if you need to do anything from Waves Central first.  Same with the Steinberg e-licenser.  Not sure.  I would just go down your list of installed products that don't have a hardware activation dongle and verify that each activation can be removed from the device just by using your online account.

Cheers guys!

You are on a Mc aren't you Fleersy? I don't know if that makes a difference. Are you on a laptop? I would rather trim the trees than burn down the whole forest. Get your laptop out and watch a few episodes of Martha and Snoops Pot Luck Dinner Party while you work.

Format C:\
 
Or you could go with the redneck method. Pull the HD and stand it up on top of the back fence, then load up the old .22 and let the fun begin.

But more seriously, HD's crash all the time. No matter the authorization scheme used, every manufacturer will have some sort of method for dealing with getting your software authorized after the original HD is no longer available. You can go through all the software and see if there is a method to deauthorize that particular computer, but ultimately you'll want to wipe/restore the drive to the original factory install. Or do the back fence .22 thing. ;-)

BobF
You should look at them as Grem suggested.  Especially iLok stuff, make sure you deactivate first.

When my old computer pooped out I just downloaded all the ilok software, installed it, then installed my plugins, popped in the dongle and everything worked fine.  I never deactivated anything.  I thought that was the purpose of ilok: use your plugins on any computer as long as the dongle is plugged in.  Have I got it wrong?  Yikes!