My old one has been corrupted due to the long usage of it.
So I'm planning on getting a new one with the back up files except
for Minecraft and Steam Games- CS: GO
I don't know the policy of both of the two companies but
If I know the accounts that I purchased the games
Is it necessary to buy the games again?
or as long as I have the same accounts then I can re download the games again?
You will not have to buy these games again. If you have a premium account on minecraft just enter it in once you download it again (or if you play online enter it where your suppost to) as that is stored in there database and with steam it should keep track of all your steam purchases on your account however steam will make you do a verification thing with your email because you are on a new computer but once you have done that you should just be able to download all your games again