iMac can't connect to 1 of 3 Windows PCs on network

I can't find any solution to this one, so thought I would try here. I have an iMac (mid 2011) setup on a network with 3 Windows-7 PCs. Since I added the iMac a few weeks ago, I have not really had any problems accessing SMB shares on all three PCs. The only issue I had is that every couple of days, the connection to one of the PCs (always the same one) would drop and it would not connect again until I re-booted that PC. However, other computers could see it fine. Regardless, I could still at least access it if I re-booted it.

A couple of days ago, the connection to this one PC was lost again, so I re-booted it. However, now, when the iMac tries to connect to it, it pops up the login window asking for user name and password. I enter both and the window just "wiggles" and stays there. I assume that means it thinks the password is wrong. The password, however, is not wrong. Even though nothing had been changed on the PC, I double checked the user account, reset the password, checked all the network share settings, tested logging into it several times, tried creating a new admin user account and connecting with that, re-booted the pc, re-booted the iMac.... nada. It just keeps asking for the user id and password.

Anyone have any idea why it suddenly can't connect to this pc, when nothing has changed? The domain is the same as the others, and I have no problem at all connecting to the others. Thanks for any help. I'm stumped.

I finally figured it out! You'll never guess what the problem was...
Something had screwed up the calendar/clock on the pc. The date was set to two days ago. I changed it to today and everything works perfectly.

LOL, sometimes the simplest things can throw a monkey wrench into the gears of progress! Glad you figured it out.