It is possible that it's your PC, but most likely the downloads were corrupted and did not complete properly. There are many reasons the download doesnt complete properly mostly due to latency or server issues but it still claims the thing is completed properly. The best thing you can try to do is to delete the files, clear your temp internet cache and try to download them again. I've had this issue happen a few times in my years of dealing with this game, the modinstaller can be rather fickle at times, but usually re-downloading the files does the trick in getting them to run.
If the three files you've tried still bug out when you re-download them, try finding the lightest (smallest) mod you can and downloading and installing that one, if it says they are all corrupted then perhaps there is an issue with your modinstaller that needs to be repaired.