Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
Office 2008 came as DVD and not as Download. You will not be able to download Office 2008 from internet. Microsoft also stopped supporting and updating Office 2008. So it is recommended to upgrade to latest Office version to work without any problems.
If you are using Mac OS X 10.10 Yosemite or later version, then you can buy Office 2016. You can buy it from here --> https://products.office.com/en-us/buy/compare-microsoft-office-products?tab=omac
If you are using 10.9 or lower version of OS X, then you can buy Office 2011. You can buy it from here --> http://www.amazon.com/Office-Home-Business-2011-1User/dp/B009SPUZCQ/ref=sr_1_1?ie=UTF8&qid=1451963770&sr=8-1&keywords=office+2011
If you have any questions or would like any additional information, please don't hesitate to ask
Office 2011 was also available online to purchase and download, but since Microsoft released 2016 version they had it removed it from their online store. So you will have to buy Office 2011 from Amazon.com or from other stores like eBay.com
If you just use Office for simple use, then you don't have to buy Office. You can just download and use this Office application --> https://www.openoffice.org/porting/mac/
I've notice you still have Office 2008 on your Mac. If you have not uninstalled Office yet, then we can try to fix Office without reinstalling it. What version of Mac OS X are you using ?
We can try to fix it first. Close Power or Force Quit Power Point by pressing Command, Option and Esc - select PowerPoint and click Force Quit. Then in Finder click on Go menu and select Go To Folder. Then type the following command and press return
This will take you to the Library folder. If you see Microsoft or Microsoft Office folder in there, then trash it. Then open Preferences folder and trash the file 'com.microsoft.PowerPoint.plist'. Then trash the Microsoft or Microsoft Office folder if you see there. Then open any other working office app, click on Help menu and select Check for Updates. Do all office updates if any available.
Open Power Point. Please let me know if that didn't work, so we can continue troubleshooting.