Pc is taking forever to open files/programs

Hi guys,
I am just bothered about my pc’s performance lately. It is taking me forever to open files and programs like Cad, sketchup and Photoshop. Every time I refresh it the screen will go blank for a while like 5 to 10secs. What seems to be the problem of my pc? I am really looking forward that someone can help me about this issue. I have deadlines to meet and my pc’s performance is making it impossible to finish my work.
