Since you said you’re using a modified version of Windows 7, I’d suggest accessing this URL in Internet Explorer (and specifically that since it uses the same networking libraries MSN uses):
https://m1.escargot.log1p.xyz/nexus-mock
If you get a download or a status page that isn’t an error, that most likely means you can log in with Messenger as normal. If you don’t, then try following this guide: