Help connecting to shared drive

I need some assistance please. I have recently run into problems where I am unable to connect to a shared drive I have with a Windows 7 PC. It was working until very recently and I have not made any changes but have problems now. I can see the shared drive and on attempting to connect I see the error message "there was a problem connecting to the server". File sharing is on on both devices, win PC has shared drive ok. I am able to connect to Mac form PC and access files etc but am not able to access files from PC. Any advice would be gratefully accepted.