Here's what worked for over a year: PC A runs Windows 7, PC B runs Windows XP. Both are on the same subnet behind a router. A uses user account X, but logs in to PC B using the Administrator account.

PC B is a Dell Precision 470. A known problem with these is that sometimes when plugging in their power cable they somehow loses all BIOS settings. This happened yesterday. After this happens Windows won't boot, because the default BIOS setting is 'RAID ON' while there is no RAID configured. No problem though, changing the BIOS settings to 'RAID OFF' makes it boot without problems. Note that in the meantime, nothing config-related was changed on machine A. It wasn't even on.

Indeed after doing this, everything is fine. Everything includes all normal operations, remote desktop from PC A to PC B, running Synergy between A and B, accessing shared folders from B to A. But accessing the shared folders on B from A does not work any more.

I tried pretty much everything I found via Google (fiddling with policies/registry kes/...) but no avail.

> ping -a 192.168.2.2
Pinging A [192.168.2.2] with 32 bytes of data:
Reply from 192.168.2.2: bytes=32 time<1ms TTL=128

> net view \\192.168.2.2
System error 5 has occurred.

Access is denied.

> net use /persistent:no K: \\A\myshare /user:A\USERNAME PASSWORD
> net use /persistent:no K: \\192.168.2.2\myshare /user:192.168.2.2\USERNAME PASSWORD
> net use /persistent:no K: \\192.168.2.2\myshare /user:USERNAME PASSWORD
System error 86 has occurred.

The specified network password is not correct.

A solution to this would be great: I haven't been able to do any work since yesterday ;]

update after taking the hard drive out of B and putting it in another Precision 470 with almost exactly the same hardware (at first sight, only the video card differs) the shared folders work.. Putting the disk back into A, same problem remains. Why does this depend on hardware, and more important, on which hardware?