How-To Geek

My new laptop runs Windows 7 professional (which I love). My desktop computer runs Windows XP Professional. The computer was purchased on Sunday and on Sunday and Monday I had no problems with the network connections. The laptop and the desktop saw each other and I downloaded files. Monday night there was a Windows update on the laptop and a Windows Explorer 7.? on the desktop. Now, this morning I am unable to see the other computer on either computer's network. I have tried running a Network diagnostic, installing a new workgroup, and removing the Internet Explorer update that was done last night. Still, the computers do not see each other, though they are both able to see the Internet router, which is what is supposed to connect them both. and, yes, I have folders shared on both computer. I double-checked that also, and that my Windows Firewall was on, but with exceptions. I am at a loss to figure out what happened between last night and today. Can you help me?