I'm sorry that your page is freezing when trying to add an image in your email. I see that you spoke with one of our Support reps shortly after you posted here, but I wanted to post here too. This sounds like it could be a connectivity issue. The first thing I would recommend doing is checking to see if you are using a supported browser. If so, try going into Private Mode (Incognito in Google Chrome) and log into Constant Contact there. Here is a link to our FAQ on how to go into Private/Incognito Mode.
Browsing in Private Mode will allow you to browse privately from any cookies or cached items that may be blocking your ability to fully access certain web pages. If your pages load fine in the private window, it is likely that there may be a cookie or cached item causing the issue. In this case, I would recommend clearing your web browsers cache.
If things do not load in private mode, I would then recommend doing an internet speed test. We recommend having the download and upload speeds both be at least 2mbps for optimal use of Constant Contact. I hope this helps.