ITunes would not let me download music properly to my iPhone 4S, can someone shed some light on how I can fix it?

Question

I recently aquired an iPhone 4S, perfectly fine, around 2 months old. everything is working fine, and all apps and music are downloaded on to iTunes and WERE origionally on the iPhone. I started to then add more songs from iTunes, though the phone started refusing to download them and then the majority of my collection were then deleted. I did origionally think that this was simply because it could not find the location of all the music files, though upon searching i found that iTunes could indeed fine every single file, and that they all played perfectly well in iTunes. I did reset the phone and try simply re-installing the exact same storage pre-reset, though it simply made all of the songs like that. The iPhone (4S, 32GB, 4 month old) did have around 900 songs on it, all playing fine, though recently the number on iTunes is around 1240, though I don't want all the songs on.
It is not that I am incapable of understanding the software of iTunes or of the iPhone, and I have had previous Apple products and also had interaction with various models (iPhone 5/5C/5S) and Android, so it this is where it stumps me on what the actual problem is.
I have tried doing things like:
Reseting the phone
Making an individual playlist with all of the songs that I want on my phone
Downloading Albums/Artists/songs/playlists individually (as to rule out if it is a specific artist/song/so on
Downloading everything and then trying to get iTunes to download the actual song directly
When updating/syncing my options on the Music tap on iTunes when the iPhone is plugged in, it registers on iTunes that the every song that I have ticked to be included in the sync has been synced, though upon checking my iPhone on the music app, the majority of the music will either have failed to sync or not be there, or be registered but unplayable (the title of the song is slightly transparent/grey). Then upon inspection of the [Settings>General>About>Songs], the count does not equate to that which is stated on iTunes.
Any help will be appreciated as soon as possible, as my iPhone is used for music a significant amount of the time and the loss of around 700 songs off of my phone is quite significant.
Bearing in mind that I am only 16 years old and have no actual IT knowledge in-depth of what is actually occuring other ethan what the consumers can see through such things as the settings and the location of files and their formats, I would be appreciative if any explanation wouldn't end up being too confusing, nor it being patronising (for instance, my ignorance of how to download music to iTunes)
Thanks, atsdkg

Answer 1

I have help for you!!!
I had EXACTLY the same issue recently. What I had to do on my PC was go into the My computer section> click on my C drive> click on users> click on my username> go into music and then iTunes> Here you should see something that says iTunes Library. Make sure that iTunes is Closed and then take the iTune library and drag it onto Your desktop. This will create a copy on the desktop but iTunes will not see it. Reopen iTunes and you should see an option to scan for media. Once you do this iTunes should re-build your iTunes library and It should be able to sync. If it syncs fine and all your content is available go to the iTunes library that you dragged to the desktop and delete it as you should not have a new one. If this does not work absolutley do NOT delete the iTunes library that is on the desktop.
Call Apple and let them know of the steps you have taken and request some help. This should fix it though!