Mac to Mac Networking Issues

I've owned my MacBook for a year and a half and have had virtually no issues and I love it. However, the last month or so I've started to have a bunch of networking issues. My wife and I run a photography business and we need to share things back and forth on our network all the time between my MacBook and her iMac. Things used to work flawlessly, and then all of the sudden, nothing works. Her iMac still shows up in my Finder window, but will not connect. I've tried the CMD-K thing with her IP address and it worked for a while, but now that stopped working as well. She cannot see my computer at all on the network anymore. However, we can both see both of our Windows computers with no problem and we can edit files on both. We have file sharing turned on on both Macs. I'm just not sure what else to do. I used to have time machine backing up my computer onto her external hard drive, and now even though that is set to sharing, it won't back up either. It won't even recognize it anymore. Any ideas cause I'm starting to lost patience. Thanks!