All right, even though the fix has already been stated, I will give a fuller tutorial, also explaining why this happens. When you try to start steam and you get the message telling you steam is already running, and you can clearly see its not, its because you steam app id isn't logged in but your steam client is running. As far as fixing goes there are a couple ways of doing things, Vista is a very unstable operating system, and windows 7 is a little new on the block, so these errors are much more common on them rather than in XP. So to start... as previously mentioned the quick fix is to end the steam process ( Ctrl+Alt-Del, open task manager, go to the process tab, look for "steam.exe" and end it ) and then re-open steam. If you want to prevent this from ever happening, you wont, now and then it will always do this on any PC. But to do the best you can you should start by taking it off your program start up list ( Open steam settings and go to the Interface tab and near the bottom, uncheck "Run Steam when Windows Starts". This means you will manually have to start it up when you start up your PC. As for when you run it, things always run better and avoid errors when you run them in compatibility mode, and as admin. So on your steam shortcut, right click and go to preferences and set the compatibility mode to windows XP sp2. Click apply or Ok, then right click the shortcut and run as admin. Running it compatibility mode should take care of any Windows related problems that are stopping the steam client from doing its business.
Have a good one, I'm off to have some Nachos,
OMG thank you i was rely woried because i have got a new computer a week ago and today steam kept on stuffing up like this so i searched google and you were the only one (that i got to look at) that acualy explaind how to fix the problem so THANK_YOU!!!!!!!!!!!!!!!!!!!!!!!!!!!1!!!
(User was banned for this post ("Dumb bump" - Orkel))