I sorted the list on most likely respective of the info you gave me. (Which is not a whole lot to work on, assuming you minecraft version is 100% legal and you are the only one using the account.)
First option is to see if you have the ports correctly filled in after the IP address. The correct syntax is
100.100.100.1:8080: the ip is 100.100.100.1 and the port is 8080. Note the ":" instead of the point.
If that doesn't solve the problem, the next thing to try is find a server that is not using your version, download that version (1.5.2 is very stable), then try and connect to it. (Don't open any single player worlds, not even the single player world selection screen.) If that works, it's a version problem: try to update or downgrade to one that works.
If that does not help, try deleting your
.minecraft folder. Make sure you back the folder up and minecraft is closed first.
- Windows: Press Windows+R, type
%appdata& and press Enter. Then locate
Many people have used this technique for similar problems without: eg. Internet connection, so the launcher could not re-download the folder. This is also the folder were world saves and texture-packs are stored so again, back it up first.
Then reopen the launcher, let it download the files and check if it works.
If that is not the case it might be that your servers are too heavy to run on your pc. What might help is setting you render distance to a lower number like 2, setting render mode to fast and turning vsync on.
Also you can make more RAM available to Minecraft to make it run faster. You can do this in the profile editor under Java settings (advanced). In JVM Arguments you will see that you can input how much ram you want Minecraft to be running on. In this box you fill in:
-Xmx2048M -Xms2048M for 2GB ram
-Xmx4096M -Xms4096M for 4GB ram
- To add more, add 1024 to the numbers for an extra gigabyte. Example: 4096 (4GB) + 1024 = 5120 (5GB)
(Remember you need to make sure other programs can still run without Minecraft consuming all the RAM, so that might be a problem.)
Finally there might be a firewall issue... which would be odd because then Minecraft would tell you. Try to take down you firewall then log on the server then turn the firewall back on. If you get thrown off, you know what the problem is. If so you can ether tweak your firewall settings or disable it for good (be sure you know what you are doing here)
If that does not help try to set up a LAN world with another PC and try logging in there (make sure you are connected through LAN of course). If that does not work it might be your way of connecting to internet which does not allow you to go online on other games as well. Do you play other games online which are not an MMORG (MMORG's have one server only which is certified)? A good game to test this is Trackmania Nations Forever because it's free on Steam and has the same way of procesing servers. If this gives the same problem you should contact your ISP.