Compaq 7540 screen is blurring and what is the reason behind that?

It could be EMI by the monitor, or it could just be failing. Try the following.
1. Do you have speakers or other electromagnetic sources (walkie-talkie, cell phones, etc.) sitting close to the monitor? If so, try moving them away from the monitor. They will effect how the electrons from the electron guns hit the color phosphors inside the monitor tube making the display blurry.
2. Try running a monitor diagnostic to check if the monitor is finally failing.
Post back how it works out.