you retain all of the ownership rights of those videos you submitted, (uploaded), to YouTube, and you have the right to delete them from your account;
"8.2 You retain all of your ownership rights in your User Submissions, but you are required to grant limited licence rights to YouTube and other Website users. These are described in paragraph 10 of these Terms (Rights you licence)."
"10.2 The above licenses granted by you in User Videos terminate when you remove or delete your User Videos from the Website. The above licenses granted by you in User Comments are perpetual and irrevocable, but are otherwise without prejudice to your ownerships rights, which are retained by you as set out in paragraph 8.2 above."
So the question is, if you still own them as YouTube say, why can't you download them back to your computer? You will need to speak to YouTube about that ad how best to do it.