i have developed c# windows application and installed it to client machine.....but it running slow on client pc.....but it runs fast on my pc.....so what to do now?

No, there is no solution for that. 

 

I have had i5 laptop and my brother had a dual core laptop. The performance for my brother's laptop was much better as compared to my i5. i5 is just a tag, nothing else! The performance is calculated by the CPU frequency. You should note the CPU frequency, also if the application works just fine on your machine you would only suggest the client to upgrade their machine.

 

On the second thought, you may consider fine-tuning your application. Which would require you to do

1. Remove any unwanted variables from the memory. Variables take many CPU cycles to create and remove from the RAM.
2. Consider removing any string concatenations being used. Instead of concatenating the string, you should use StringBuilder to build the strings.
3. Use Visual Studio's application profilers to see how much CPU and RAM is being used in which functions and then fine-tune them to make it better. 

Most of the times, the application acts bad because of the architecture being used. If application uses network resources or other similar stuff, and has a graphical user interface. I would recommend that you use Asynchronous Programming model.  It would let you make the application process smoothly.