@Skyro, good news.
You are correct about first trying a simple "repair" using the normal "Add/Remove Programs" method.
Apparently, other AV tools that may had been uninstalled in the past were not the problem, since the OP has been using Avast for some time now, with no problems.
The OP (Skyro) already tried "reinstalling" using a new downloaded setup.exe, which failed to solved the problem. That means that the problem may need deeper investigations than some repair using the normal "Add/Remove..." method.
Many things could be tried to actually solve the problem (and learn from it so to avoid it in the future).
The "workaround" is much more efficient and effective in this case. After the OP already tried the normal repair but failed, this was the faster "solution".