How do I enable cookies on Windows 7?

Cookies are not enabled in Windows 7, but in whatever browser you're using to access the Internet.

It's a bit surprising that when you visit the website you didn't get a pop-up window asking if you would agree to permit cookies.  Perhaps you did and said no.  In any case, you can change the setting.

Assuming that you're using Internet Explorer, click the "gear" icon in the upper right corner of an Internet Explorer window and select "Internet Options."

Click the "Privacy" tab.  You'll get this window:

You can adjust the overall security setting using the slider, but you probably should not do that.  Instead, click the "Sites" button and enter the address of the web site in the box and then click the "Allow" button and then "OK".

If you are at the linkedin website when you do this, as soon as you start to type linked ... the correct name will be automatically filled in:

Once the name is correctly entered, click the "Allow" button. 

After you click "Allow" the name of the web site (without the http://www part) will appear in the bottom window.  Click OK.

If you're using a different browser, e.g., Firefox or Chrome, the procedure will be slightly different.  If you need help with one of those, tell us what browser you're using.