Please read through all of the information below before trying anything.
Just so you know many computers come with office as a Trial version, usually 30, 60 or 90 days. You do need to buy office and it does not come free or anything.
When you bought it you would've received a license key, it may be a sticker on the computer or with your documentation. PC world would have given you that and the license key is essential, you cannot use office without it.
So before trying anything I list below you should confirm that you own office and have a the license key. I am not sure how PC world handles it so you may want to give them a call and see if they would have given that to you. Also if the computer is under warranty with them call them first before trying anything I list below.
What you can try is a system restore back to a time when it was working. System restore does not affect your personal documents but it does revert the system and program files back to an earlier time. So please understand that before trying this. It basically means if you installed a piece of software in the last couple of days it will be removed by using system restore, everything else will be the same.
Here are the instructions on using system restore and I cannot stress enough that if you choose the wrong option you can cause major damage so you must follow these precisely.
Swipe in from the right edge of the screen, and then tap Search.
(If you're using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, and then click Search.)
Enter Control Panel in the search box, and tap or click Control Panel.
Enter Recovery in the Control Panel search box, and then tap or click Recovery.
Tap or click Open System Restore, and then follow the instructions. Choose a restore point that is before the issue with office happened.
Let it finish and try to open office again.
If that does not work it is going to need to be re-installed but you will absolutely need the license in order to re-install it.
If you do have the license key follow the instructions on this page to reinstallhttp://office.microsoft.com/en-us/products/download-back-up-restore-microsoft-office-products-FX103427465.aspx
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