There are have been some speculations that some ME2 saves cannot be imported by ME3 because those saves uses DLCs in ME2 (such as Overlord or Shadow Broker). Will reinstalling ME2 and those DLCs help?
Having the DLCs installed or not installed should not matter, as Mass Effect 3 only draws from the file directly, and does not actually check your installation.
I have a character file with all the DLCs installed and played and she imports fine (minus her face mesh, for whatever reason) just the same as my current playthrough, my vanguard, who never got around to installing and playing the DLCs before ending his career.
The only thing that matters is that you have MAss EFfect 2 save files after the "ending" of Mass Effect 2. DLC doesn't matter in any way, you can import any save with/without any DLC as long as you reached the end of ME2.
It's also important that Shepard didn't die during the ending
The save files should be in My Documents\Bioware\Mass effect\Save, if they're not in that folder the import won't automatically find them. If you uninstalled Mass EFfect 2 it might have removed the save files (I really don't know) so check and make sure those files exist.