Will you please provide us with some details so we can try to help you?
1. 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. Can you access any of these directly?
2. Are you using http:// or are your using the secure recommended https:// log-in? see > http://en.support.wordpress.com/https/
3.Exactly which browser and version of it are you using? If you don’t know click here to find out > http://whatsmyuseragent.com/
4. Have you tried clearing your browser cache and cookies? http://www.google.com/support/accounts/bin/answer.py?hl=en&answer=32050
5. Is your browser version up to date? And is it the latest stable version as opposed to a buggy BETA version? You can upgrade any browser version here. http://browsehappy.com/
6. Have you tried using the browser with all extensions or add-ons disabled?
7. Do you have third party cookies enabled? http://support.google.com/accounts/bin/answer.py?hl=en&answer=61416
9. Do you have another browser you can try?
10. 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/
11. Have your tried resetting your router and modem?