It could be the display performance settings—let's start there. Try View > Display Performance > High Quality Display. Do they look better?
If not, take a look at Window > Links, which lists the linked graphics. Do you see any yellow triangles or red circles after the file names?
Come back to answer these questions, and we can go from there.
Thanks so much for your response. Here is a screenshot of the low quality if this helps. I sent this music as PDF's to my original designer who kept the quality high. Then she sent me her .indd files, and another designer is showing me that they look like this, blurry ;(
Ok, so do you see the red circles in the Links panel? They indicate missing graphics, and that is why you are seeing the low-resolution images on the page.
The original designer should have used the File > Package command to gather up everything that you need to republish the book. This includes copying all of the linked images, and relinking them from the new project folder. The red circles either indicate that the designer either just returned the InDesign file and not the images, or perhaps you moved the InDesign from the folder she provided, which would break the links.
The next step is to examine what she returned to you. Is there a Links folder with all of the images in it? If so, let us know and we can help you relink them. If not, you will want to return to her and ask her to package the file and resend it along with all of the assets.
The placed images is missing you need to update it.. while sending the indesign file she has to send with the original folder not only the indesing file it should include the images too which has placed in indesign. so ask her to the send the images and make a folder Keep the .indd file and images in one folder and open the indesign you will see the result.