Intel HD Graphics 4600 is part of the Haswell processor family. These can, in principle, support three display devices. However, it doesn't depend solely on the processor.
Quote from the official processor description:
"This feature may not be available on all computing systems. Please check with the system vendor to determine if your system delivers this feature, or reference the system specifications (motherboard, processor, chipset, power supply, HDD, graphics controller, memory, BIOS, drivers, virtual machine monitor (VMM), platform software, and/or operating system) for feature compatibility. Functionality, performance, and other benefits of this feature may vary depending on system configuration."
Who manufactured your PC? Can you provide the make and model?
