Final answer:
Among the provided options, a corrupted bootloader and an overheating CPU can prevent a system from booting up. While insufficient RAM does not typically stop a boot process, it causes performance issues, and an outdated antivirus does not usually affect booting but may lead to security vulnerabilities.
Step-by-step explanation:
A system can fail to boot up for several reasons, but based on the options provided, a) Insufficient RAM is unlikely to prevent a system from booting, though it can cause performance issues. b) A corrupted bootloader is a common reason for a system failing to boot because it interrupts the startup sequence necessary to load the operating system. c) An outdated antivirus will generally not prevent a system from booting, although it can cause security issues. d) An overheating CPU can cause a system to shut down automatically or fail to boot to prevent damage to the hardware.