Windows server 2008 r2 standard is connecting 24 cilent machines
What do you mean with this?
In Windows server 2008 r2 maintaining the mysql database and all other client
machines are pointing to mysql database server.
So, you are not talking about Windows here, but MySQL Being slow.... so, let's have a look at your machine... OS; Processor, RAM, but NO WORD ABOUT DISCS.
It is likely a combination between non-competent programming and unsuitable hardware is the culprit.
Bad programmed databases eat tons of IO (and good ones still need a lot). So the most important thing on a database server are the discs. Realize that you say nothing about them?
Depending what you do, you may need between 2 and 2000 SAS discs (or more) to satisfy the IO demands - the number of users is irrelevant unless you can specify what they do. Heck, I am loading a similar server (a little smaller) to the max at times with 3 users (and 200 machines pushing data) and that is a sevrver with about a dozen SSD for the database.
So, stop blaming windows - start analyzing where the load is spent and then start looking at your discs and mysql configuration.