Steam is already running in another user session...

[NDORFN]

Something like that. It's been happening to me quite alot lately. Anyone else been getting it?

[buzz456]

I am presuming that you don't have two computers with Steam on them. I wonder if your Steam account might be hacked? I had this happen (got this message) one time a couple of years ago. Signed off Steam and got back on in a few minutes and never saw it again.

[OldProf]

I also see this from time to time and I'm only running TS2013 on one computer. It tends to happen when I try to start Steam after it has failed to load during the boot-up process, which makes me think that the boot-up load didn't fail at all. Regardless of the cause, the easiest way I've found to work around it is to restart the computer.

File this under "mysteries of the RSC parallel universe".

[NickF]

Look in Taskmanager and see if the Steam process is running. If it is, kill it and restart the Steam client.

I've also seen this happen when another Steam-based game program didn't shut down correctly.

[alanch]

Regardless of the cause, the easiest way I've found to work around it is to restart the computer.

The Steam process doesn't always stop running when you close down the Steam client - you can always check by running the Windows Task Manager and looking for the Steam.exe process. Right clicking on that will give you the option to End the process - ignore the warning and go ahead and close it, and you should be able to restart Steam without rebooting.

EDIT

Nick beat me to it.

[NDORFN]

Cool cheers guys. I didn't think it was a major.

[arizonachris]

I don't know how you have your Steam client set up, mine starts when Win 7 starts. I get a little icon in the tool bar, down in the right side. I always have Steam running. I did have my account hijacked a few years back, took support a few days and I had to prove who I am, to get the games back, but they did it. (I only have 70 games on Steam)

Someone on another PC could be using your account. Who else has a PC that knows your account name and password?