Yes assuming you've launched the game once, when you first launch a Ubisoft game that requires uPlay from Steam uPlay should be installed with it, an account must be created (or logged into), then uPlay will ask you if you're sure you want to link the game key to your account before you can play through just uPlay.
Once that is done you should be able to ...
Type "services" into the search box
Type "Steam" - now "Steam Client Service" will be highlighted.
Set "startup type" to manual.
Press CTRL SHIFT ESC. "Task manager" will appear, and open the "Startup" tab. Look for "Steam Client Bootstrapper", click "disable".
TLDR; create or modify your current game's appmanifest file (in your case appmanifest_356190.acf) in your Steam\steamapps folder, and adjust the following values:
StateFlags to 1026,
LastUpdated to 0,
UpdateResult to 4,
SizeOnDisk to 0,
buildid to 0,
LastOwner to <identical value>,
BytesToDownload to 0, and
BytesDownloaded to 0.
Remove the ...
There should be a folder called Program Files/Steam/Steamapps/downloading which contains files currently being downloaded. You'll need to start the download on your new computer, pause it, get the files off your old computer (from /downloading), navigate to Program Files/Steam/Steamapps/common/Rainbow Six Siege, and put the files (from the old computer) ...
Is the game folder for Steam in the Program Files directory? That can have some issues with Window's UAC (User Account Control) and should be avoided if possible.
If the issue is not related to a firewall like the other commented suggested and is instead a hardware/software issue, you may want to consider trying OpenMW as a modern engine replacement for ...
Try adding the Morrowind executables as exceptions to your anti-virus software (and firewall).
Cross-referencing both issues (Steam thinking the game is still running and the InstallShield Engine iKernal (unregistered) class problem) that approach is what they have in common.
Steam having this particular problem with Morrowind seems to be more common, and ...
You need to contact Steam support directly in order to recover your account.
Follow the instructions in the steam account recovery guide.
You will need proof of ownership, this can be for example one of the payment methods that were used to purchase games on the account.
A full list is in the linked guide.
Also make a list of any previous account names ...
It's basically the same price as buying everything standalone. I've seen this being drive by multiple games when the season pass is actually a "DLC" itself rather than just a bundle.
This is most likely due to third party keys being involved. Don't worry, you're not paying twice for it.