White Screen in Admin

I just noticed that i cannot log in to my multi-site install. The wp-admin url is just a white screen. It happens using the main site url and any of the sub sites in the network. I have domain mapping so each sub site has its own url. I have recently changes IP address of the server but i use cloudflare and updated the ip in the DNS settings for all domains. The front end is all working fine and people are using it so i dont want to deactivate plugins, i.e. break the site if i dont have to.