Takes Long Time to shudown or restart your Computer/Laptop/PC

Maybe there is a malicious software accidentally installed in your operating system.
If you’re using Windows XP/Vista/7, hold Ctrl+Alt+Del to open Task Manager. Go to Process tab and find out whether there is any program that cause high CPU usage. Kill the process. If you think the program is malicious, then delete it (Use the Search function).
Better to install a good anti-virus software once you just installed an operating system.
Perhaps, your hard disk is going to die soon.