Why are my images in my brochure blurry after EXPORTED as PDF?? Was clear before but now blurry on print and Indesign?

I was given a previous Indesign brochure to edit. I edited the fields, saved and then exported as PDF. Once I exported, my Indesign documents images all turned blurry. Why did this happen and how can I fix it? Im almost positive when I went to print and or re-open the brochure that it prompted me saying i was "MISSING LINKS" and I chose to ignore. IS that causing the problem? And if so, how do I fix? Im on a time limit for work.

Please help!