I used to be to sign into iTunes and see all of my music on my home computer. I have not been on iTunes for a long time. I cannot find where my music library is located. If able, please advise. Thank you!

When you say "sign into iTunes" you make it sound like you are signing into the iTunes Store using the iTunes app on a mobile device. It infuriates me Apple used the same name for two different things since it is also the name of an application on a computer which does a lot more than the mobile app. I presume you are talking about starting iTunes on a computer.

You do not need to sign into anything to see the library on a computer. It should display when you start the iTunes application. The location should not get lost unless you have changed computers or swapped drives, or moved files around a lot. If you have done that then you will need to do a bit of searching yourself. Now you say "PC" which makes me think you are using a Windows computer (this is the iTunes for Mac forum). If that is the case quit iTunes and start it again while holding down the shift key. When prompted, navigate to the iTunes folder and select the iTunes Library.itl file in that folder. A library is really a whole bunch of files and folders but that is in essence the iTunes library file that ties it all together.