How are you connecting to the internet and to WordPress.com? The way you connect to the internet (mobile, satellite, DSL, dial-up) and to your blog, and how many proxy server jumps etc. it takes to connect can cause problems. There maybe be problems with your ISP and/or with the proxy servers.
Are you using http:// or https:// see http://en.support.wordpress.com/https/
Which browser and version of it are you using? Have your tried clearing your browser cache and cookies? http://en.support.wordpress.com/browser-issues/#clear-your-cache-and-cookies
Is your browser version up to date? You can upgrade any browser version here.
http://browsehappy.com/
Do you have third party cookies enabled? Do you have another browser you can try?
You can use this link to see if your Flash is up to date. http://www.adobe.com/software/flash/about/ If it’s not up to date then this is where to download and install the latest version of Flash. http://www.adobe.com/products/flashplayer/