Server not accessible after yum update of centos 7

Hi
I did a yum update of centos 7 and now I have two major issues.

1. yum no longer works as there is a missing module
2. I can not access my websites or Plesk in normal boot mode nor can I use putty. However, I can access my server in putty in receive mode.

I'm assuming for the second issue there's a problem with the firewall? and the first issue seems to be well known on the web but not easy to fix.

I've use Filezilla to sftp all my servers down to my local computer.

Can I just reinstall my OS from scratch and then upload the server files or is there some other way to fix this.

thanks
kevin