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If you're on a network and have opened files from the network, check this Microsoft Knowledgebase article: An Office program is slow or may appear to stop responding (hang) when you open a file from a network location. Check Tools, Options, the Save tab remove the checkmark next to "Save AutoRecover info every xx minutes. As a rule, add-ins won't cause PowerPoint to run slowly once it's started, though. Do you have lots of add-ins loaded? Each add-in will slow PowerPoint startups down, some more than others. Another user reported that he found hundreds of WMF files in his \TEMP folder and after deleting them, PowerPoint started up in seconds rather than in minutes. Check your \TEMP folder for excess files. A PowerPoint user on the newsgroup reported that installing the most recent service pack for the version of Office in use and setting up Outlook personal folder files so they are no longer using compressible encryption speeded PowerPoint up considerably. If you run Outlook, turn the journaling feature off.
Shut down PowerPoint and all of your other programs then restart your computer.PowerPoint starts and/or shuts down very slowly, takes a long time to open files, bogs down when you're entering text, etc.