Try starting Task Manager. Click on the Process tab then click on the CPU column header to sort bu CPU Usilization descending. Leave the window open and move it off to the side a bit so you can still see it then start using Word or whatever you need to see the problem. You may want to install Process Monitor
to see if it gives you more/better information that Task Manager does.
When it occurs, look at Task Manager/Process Monitor and see if it gives you any indication of what is causing the problem. My guess would be something you've installed recently or malware. May want to do some scans with your anti-virus program and Malware Bytes Anti Malware (free version), see if they show anything.
ANother way to troubleshoot this: How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7