What to do if my system is not at all booting?
This software actually works fine even when system fails to boot, but you still need to find a healthy computer and download this software.
If you cannot boot into BIOS either, please remove the hard drive and connect it the healthy computer as a secondary drive, then backup the essentials after you had a deep virus scan on it, and run ByebyeData Eraser > click Entire Disk tab > select the new connected drive > choose a wiping plan > Erase Now.
If you can boot into BIOS, then use WinPE ByebyeData Eraser, which can be created on the healthy computer, and repeat the steps staring from clicking the Entire Disk tab.
Note: The virus scanning on the hard drive step is necessary when the disk fails to boot on the previous computer, because that mostly due to the boot sector is affected by viruses. In most of the case, security software will detect and scan the new drive automatically, but you can also try it manually when anti-virus program fails to run too.
Go through the hard drive and find important files to backup is also needed before erasing, since once ByebyeData Eraser starts to overwrite, there's no way to get data back. This is not what we said, but all the data recovery programs' FAQ section emphasized.