wordpress white screen of death (fatal error)

[McCloud]

So I am having some issues with my site lately.. not sure what caused it, but when I opened the website, I could only see a blank page (with empty html) - I already tried all 'white screen of death' suggestions without success.

After the advice from my host, I changed to another of their servers and completely re-installed WP. It worked fine for a while.. then I copied back the wp-content and I get the blank page again.
However, when logging in (/wp-admin) I get this message:
Fatal error: Cannot redeclare win_is_writable() (previously declared in /home/u363187447/public_html/wp-includes/functions.php:1672) in /home/u363187447/public_html/wp-admin/includes/misc.php on line 557

I can see some directories, but no idea what it means..
Is there a way to repair the files ? Any advice is really appreciated.
Thanks.

[SnakeDrone]

Your theme is bugged. Possibly caused by different WP version on the new server.
Try deleting the themes folder from the server. You should be able to login after that.

And then comes the fun part of tracking down the bug <_<

[McCloud]

Deleted the themes folder, but get the same error. 

[SnakeDrone]

Is the old and new wp the same version?

[McCloud]

Is the old and new wp the same version?

good question. I don't think it was, since I used the Cpanel on the hosting, which installs an old version.. then I updated straight away directly from wp-admin control panel. Could that be a problem ?

In that case, do you suggest to re-install WP in the same version as the old one was and only then replace the wp-content folder with the old back-up one ?

[SnakeDrone]

If your domainname didn't change, I would recommend to transfer all files from the old to new server and then copying whole database over then update new database info to the wp-config file.