Sometimes it works, sometimes it doesn't

[spindoc]

I have a Buffalo Linkstation LS-GLC65 1tb external hard drive hooked up to my network.
For a few years it worked just fine.
One day I changed my modem and router and since then I've had nothing but problems.
I turn on my computer and can't access the drive, I get the error:

\\LS-GLC65\share is not accessible. You might not have permission to use this network resource. Contact the administrator of this server to find out if you have access permissions. The specified server cannot perform the requested operation.

Then an hour later, after not doing anything at all, it works. I can access the drive, use files, everything.

Then 15 minutes after that, it stops working again and I get errors. When I go to NAS Navigator, I can do an IM HERE, see the drive, but there is no share.

When I open up the navigator in the browser, the share is there, but I can't access it.

Then half an hour later, I can access it. works just fine.

Makes no difference if I reboot, sometimes it works sometimes it doesn't, after making absolutly no changes to windows or network.

Whats the deal?