If the stick is fine then:
i. Hardware driver is not compatible/corrupt. Update all driver
ii. Bad sector on HDD (which accidentally damaged the software/driver thus the wrong string is injected into boot sequence causing the failure). Refer to Scandisk or use the Tool > Error Checking with bad sector recovery ticked through drive's Properties tab.
iii. Software i.e antivirus is behaving badly or a virus is behaving perfectly. Scan the disk or re-install the antivirus.