Having HDMI issues

When you plug a TV in to HDMI on a laptop one of two things should happen first off.
a) the TV should be recognized and turn on while the laptop screen turns off or
b) the TV will be recognized and turn on and the laptop screen will stay on as well.

Assuming the latter has happened in your case there are a few things that could be happening due to what information you have given us so far.
My guess is that your Laptop is configuring the computer screen to be in a dual monitor landscaped mode as hang-the-nine states.
This will mean that your laptop and TV are both part of a panoramic view for your desktop now and in order to get your brain wrapped around the idea of how its working if you've never experienced this before you need to determine which one is on the left and which is on the right. Moving your cursor off the left side or right side of one screen will usually be all it takes to figure this one out... but again if you never experienced it I guess it could be a little odd. Setting the laptop to the left or right of the TV might be helpful if this is really an issue. LOL

First off to go any further you need to know how to access your video configuration options.
This is where you need to start.

I would suggest to make this simple on everyone and you unplug the TV for this step. (unless of course your laptop screen is broken in some way and you can't)
With the TV unplugged you should have your good old laptop back to normal cursors on the right screen and all.
Go down to the lower right hand corner of the task bar by the date and time and find the little arrow that opens the system tray. There should be an icon for your Video Settings in this area someplace. Hovering over an icon should tell you what it is exactly if your unsure.

Another way to access it depending on whether your computer manufacturer decided to include it here is usually just by right clicking anywhere on the desktop and scrolling down to your video adapter settings. Sometimes you have to choose the Display Settings option before there is a way to get to your Video Adapter Control settings. This is usually dependent on how easily they made it to be found going this route. I'm not sure because I don't have a lenovo and you didn't give us the exact model number to look it up for you.

In any case when you have found this that is where you will be doing all the adjustments to make everything work perfectly for you. You can choose to use both monitors as a mirrored output meaning the TV and laptop screen display exactly the same thing. Or you can choose to span your displays usually landscaped and portrait spanning are options and you can pick which you want as the Primary Desktop and which is just a secondary work space. Or you can set it to output just to the laptop or the TV. You also should be able to adjust all the resolution settings in order that the picture is the right size in there as well.

One thing I suggest you try that might be a quick fix to all issues as well is to plug in the TV and restart your laptop.
Sometimes this will detect the TV at startup and override the laptop screen completely just giving you a picture on the TV. I'm not sure this is what exactly will happen as I don't have the laptop to test it out myself... but it may do the trick.

I'm not sure what the outcome your wanting to achieve by plugging it in to the TV other then when you're home you can have a big screen experience with your laptop which is all the reason to want to do this in the first place.
A lot of people prefer the dual monitor setup for productivity or just watching a movie on one screen while doing work on the other.
There should be plenty of settings to adjust your screens in the graphics settings panel to suit your specific need.

If you can't figure everything out from that point ask away. Just please give us a little more information next time and try to be specific if you could.
-John