Restrict Application Execution after a specific count

ok, first of all what you asked is not possible without each computer having internet access.
first way is to create a database in a central computer, check the initialization count and update a table each time the program runs. this is the easiest and most convenient way.
another way is to put the power of cloud to use. create a microsoft skydrive account. create a file there that stores how many times the program had run. on initialization of your program, download that file using skydrive .net api link, update it, and upload it. do not forget to encrypt the file contents to prevent tampering with it.
if you do not have any means to operate a central server or skydrive, as an alternate way, you can use google docs. this is a long way and not optimized in any means, but its what comes to my mind now. using google docs api, store how many times the application had run in a spreadsheet.
as a funny way, create a twitter account and tweet zero. on opening the program, read the final tweet and retweet the update using twitter api.
I'd stick with skydrive though