sounds like a virus has infected your PC and added bytes to files. mIRC will not run if its been modified in any way. And it sounds like the virus is preventing msconfig from running to attempt to stop you from preventing it loading at boot up.
Theres a thread somewhere on the forum with links to online virus scanners, i'll post it in a second when i find it.
[Edit] here we go:
https://forums.mirc.com/showflat.php?Cat=0&Number=79354&an=0&page=0#79354
