The biggest problem is that you did not search for an answer. The problem you are getting is perhaps the most common one people get, specially newbies. All moderators and some users are quite pissed already having to read over and over the same question. Instead of an answer, all of you receive is a very unkind welcome to the forums because you did not follow the rules (search before posting + provide relevant information).
Just try searching for "uses an invalid compiler [YOUR ANSWER IS ALREADY THERE. SEARCH THE FORUMS!]" and you will see what I am talking about. I get 8 pages of the same thing. People asking over and over and over again (I even think that many of those questions were deleted). 8 pages of that have become noise in the forums, and those few who search will have to go through many posts before they can reach the answer.
I have already said here that the error message that Code::Blocks shows to the user is vague, and, specially, confusing to new users. The message has been changed in an attempt to make it clearer, but I still believe it is not clear enough.
Guide to an answer:
The message says that there is a chance that something is not correctly configured in the compiler options: the toolchain path. If you go to the compiler options there is a tab somewhere with the paths and names of the tools that make up for the whole compiler suite. You must check that the path is correct, that it points to an existent location, and that the names of the compiler tools name executables in the bin folder of that path.
You said you uninstalled programs, so there is a chance that the path to the compiler is no longer valid. Maybe it was pointing to an old compiler you just deleted, or something.
Please, check that information, try again, and report back what was wrong (what was the path before, what it should be, was a tool name not found, ...).
Also, please, do search before posting (as a general rule here and everywhere else).