Cant play anything, cant connect with library, cant re-install

Question

Hi, hopefully someone can help me, sorry this so long, seems that everything has broken down...
1. Last night I was trying to correct a few things in my library e.g. where itunes had wrongly split 1 album into 2 etc.. I assumed this would be straightforward but wish I hadn't even attempted it now...
2. When I tried this for one or two albums and synched to see if it had worked, I was receiving error message like: "... won't play because it is not authorised on this ipod" and "... could not be located".  The songs had exclamation marks next to them and wouldnt play
3. I googled some solutions and tried various things such as editing the "Get Info" details and re-pointing to the library, but in the end this just resulted in none of the files being located
4.  I kept looking for solutions online, and tried various similar things such as collecting all music into one file, replacing it into the iTunes folder and re-pointing the library to it (in "Preferences") and re-synching but that still didnt work
5. Then eventually nothing would play - not in iTunes and not on my ipod either - i.e. the songs were there but when I clicked play nothing would happen
6. Eventually the synch removed all of my music off my ipod except what I had purchased from the iTunes store (so that is on my ipod but wont play. The podcasts wont play either)
7. So next I tried to uninstall iTunes, re-install and recreate the library by pasting all the files back in.  But I can't re-install it.  The first time I re-installed it told me it couldnt find "Apple Mobile Device", and to uninstall and reinstall again.  I did this but now everytme I try to install I get an error saying I can't because an installation is already in progress.  I've googled for a solution and tried running "clean disk", restoring the system to before I'd unistalled etc.. but nothing works..
I'm not sure if this is related but a few months ago my hard drive was replaced.  I recovered all my music and had managed to get things working but perhaps it is related if the original music files weren't in the places they were supposed to be or that iTunes was expecting??
This also may be unrelated but for a few months now, whenever I try to sync I get a message saying "scan and fix" or "continue without scanning".  If I choose scan and fix it crashes my PC, so I just used to choose continue without scanning and it would sync correctly.
Can anyone help?? The first thing I need to do is reinstall itunes I suppose but at the moment I cant even do that...

Answer 1

Ok, seemed an antivirus program was preventing install, so that bit is sorted
The problem now is that I cant import my old library.  I imported these files from CD a few years ago.  More recently I found one other old CD and have purchased things from the iTunes store. The CD i added recently is there, as are my iTunes store purchases, but I can't import the rest.
Is there anything I can do?? They wont play in Windows Media Player either. Could there be a permissions issue??iTunes file formats changing in updates and now it doesnt recognise the old ones??