My "u" key on my laptop keyboard doesn't work. How do I fix this?

Ok, Try cleaning under the "U" key with canned air. the simplest answer here is that something is keeping the key from pressing down on the membrane that types the letter. The next step would be to remove the key and clean beneath. Unless you know what you're doing, don't do it; get a tech who knows how to remove the key. Once cleaned and replaced, see if this fixes things. If it does not, the keyboard will need to be replaced. This is not a setting, as it is only one key. a good tech can replace it easily. softlay.com

It is unlikely that this is a configuration issue.  Sticky key or the likes would affect all the keys, not just one.

When a key stops working like that it is usually because there is dirt of something under the key that is preventing it from being able to be properly depressed.  Try blowing it out with some compressed air.  

Not familiar with Lenova keypad to be able to predict if you were to pop the key off it you could get it back on.

Replacement keypad usually run in the 30% range.  You can get one off Amazon or most other sites like which sell computer parts.  

If you are nor comfortable replacing it yourself, most repair shops will do it for you for another $30 in labor.

a pc is a dust collector so you keys stop to work and fan stop cooling you have to dust your pc out with compressed air ,  he will be new again

Just replace all words that involve the letter 'u' and find a suitable synonym that doesn't have that letter.

TURN OFF THE LAPTOP FIRST, then Try using a very thin nail file and see if you can't pry that key off. Likely there is something under it that is causing it to stick and not work right. Clean it out. Then gently press the key back into the space. 

And BTW: "sticky keys" has nothing to do with actual keys that "stick."  What that function does is let you repeat a single letter very fast. Sticky Keys isn't about the KEYS--it's about the typing. You don't have to disable anything like that. If you can't get the key off, then take it to a computer store or repair place, (i.e. like Staples) and see if they have a tool that will do it. They likely will. 

It's either worn out or dirty.

The easiest fix is to get a USB keyboard. 

you cant fix it , take it to a repairer , its either a sticking key or a faulty electrical part , either way the keyboard has to be removed .

Often a bit of debris gets under a hey and gets into the scissor (or butterfly) mechanism . Keyboards are notoriously just gross about trapping all kinds of crap. I hated cleaning them out when I worked on them. If it is just a key or several that has become unresponsive and it is this, then a can of compressed air can usually free this debris and all will be fine. If it is something else like the dome cap switch it actually is contacting on the board then is could be collapsed. Sometimes I have fixed this with freeze spray (used for searching a thermal short on a circuit board. It could also be in the board itself as the keys may be in a daisy chain type setup and several are connected together. This can sometimes be fixed, at least temporarily, but usually it is better to discard it and get a new keyboard. On many keyboards it is just a pad that make contact with another pad on the bottom of the key itself. Sometimes a contaminant creates resistance and a cleaning with isopropyl alcohol on the contacts will cure it. It all depends on the type of keyboard you have. Sometimes it can also be from a faulty driver (rare but it has happened on special keyboards).

Have the laptop checked at a Lenovo service center.

the membrane underneath that makes the keyboard work is damaged.  probably through wear.  you need a technician to replace it, but be certain to ask the cost in advance -- depending on the age of your laptop, it may not be worth fixing