Reply to DavidR (and ll of you also who bothered to reply, thank you, all, it is so much appreciated!
I did it because whenever my c runs slow avast always detrcted everything properly and solved problems, I mean ehy I m running the boot scan. But this time it never finds viruses, malware, any problems and it became so suspicious to me so i decided to run the boot scan. And it found many msny many problems, from corrupted files to windows sysyem errors.
I v deleted the corrupted files and rerun the boot scan and then it found only already existing system errors, as corrupted files were deleted so it couldnt detect them ny longer, naturally.
Then in order to recheck i v listened to the threads at microsoft forum and I v learned how to scan the software there and I did. The results were tge same as the results of the boot time sAvast scans, the very same system32 erorrs detected and shown. O Avast detected the real, existent, system errors which make my wibdows run way slower. Now I wanna fix it all but i donr know how honestly, and I dont want to reinstall windows all over again to be honest.