Inspiron 8500 Monitor Display Problems

I just bought an Inspiron 8500 and a port replicator.  I hooked it up and the image on my Sony Trinitron Multiscan 500PS is so blurry it gives me a headache.  Even though the monitor came with an old Dell computer I bought, Dell has thus far been entirely unhelpful.  The Sony web site only addresses issues with Windows 95 ( I think with this monitor, but can't be sure because of the way they describe it), so I'm thinking it may have something to do with Windows XP (?) (my current operating system).  I try Microsoft and they direct me to Dell.  Can anyone tell me why my image is blurry and if it can be fixed?  [And if yes, how.]  I had an old NEC monitor hooked up before and it had the same problem.  Thank you in advance.  I'd really appreciate any help!