What version of Windows? Is this a normal install of Windows or did you do anything different/custom?
Assuming Windows 10/11 try disabling Real-time protection (Virus & Threat Protection / Manage Settings / Real-time protection) at least temporarily during the install.
Also disable any other anti-virus/malware type software you have.
With all of that disabled re-download qBittorrent from the normal download sources https://www.qbittorrent.org/download
When you attempt to run the setup make sure to run it as administrator so it is elevated (do a shift right-click on the setup.exe file & select Run as administrator).
If the install finally works, before you re-enable Real-time protection you should add the installed qbittorrent.exe in the Windows Defender Exclusions and Controlled folder access (Virus & Threat Protection / Manage Settings / add or remove exclusions) and (Virus & Threat Protection / Manage ransomware protection / Allow an app through Controlled folder access). The installed qbittorrent is probably in C:\Program Files\qBittorrent\qbittorrent.exe or wherever your programs are normally installed.
If none of that worked then I'd go with the other commenters, run RAM and hard drive diagnostics & make sure that's all working correctly.
Or maybe your Windows OS install is broken somehow, I'd run sfc and dism in those cases (a bit outside of scope of this community but you can search around for that).