catalogues are saved on my C drive and photos themselves saved on C drive and also external drives.
Do you have a backup saved on External Drive?if so try opening that
Or Start a search on your Computer for " *Lrcat" and then open the catalogs in result one by one
Re-installing and uninstalling will not help this problem.
You need to find the most recent version of your catalog file and open the catalog file in Lightroom. Use File->Open Catalog.
The reason the thumbnails are grey is that Lightroom can't find the photos, you moved the photos to a new drive. You can fix this problem by using the Find Missing Folder command, see Figure 4 in these instructions: Adobe Lightroom - Find moved or missing files and folders
i try to start the lightroom program from the external drive and it says program can't start because amtlib.dll is missing from your computer, try reinstalling to fix? The one I have just reinstalled on my hard c drive does not have this error. I know I have to create links to where photos are now but I know its not my most recent catalogue because my keywords are not up to date and the greyed out areas in number do not match the kind of number of images I would expect, when I have found missing folders it does not increase the number of photos.
I don't see any value in having Lightroom installed on both the C: drive and on some other drive. Just use the installation on the C: drive.
Your problem again boils down to finding the right catalog file to use, and fixing the links. Re-installing Lightroom will not make a difference here.
i forgot i had it installed on external drive and reinstalled on c drive as my programs were wiped out, if i uninstall the one on the hard drive will it create problems?
This is uncharted territory for me, I don't know what would happen if you uninstall one version.
However, it seems to me your concern is still uninstalling, which isn't going to fix anything; rather than finding the most recent catalog and then fixing the links, which will solve your problem.