Cannot use MS Office 2013 after latest W10 update

Hello, I am new to this forum so my apologies if this is not a new W10 issue.
I have been using W10 on my Dell Vostro 15 laptop, 3000 Series, for about 15 months. When I got the laptop I also installed MS Office 2013 and have been using it for the last 15 months or so without any problems. I got Office 2013 from a reputable vendor. It is original, genuine and legal and registered to me and properly activated. About a week ago I successfully installed the latest W10 update but since then I cannot use any of the Office 2013 products. Each time I go in to Word or Excel it initially opens up but then a small window displays briefly and the program then closes down without any warning.
Can anyone advise if this is a known problem and how I go about getting it fixed? I have been trying to contact Microsoft but don't know how to do so. Does anyone have a telephone number for Microsoft so that I can log this issue with them? Thanks!

Thanks Kari - that resolved the problem. I had to reinstall the key and fortunately had that to hand. I really appreciate your help. Thanks!