Statement: Only Peripheral are Computer. Some Hardwares are Peripherals. Some Hardwares are Devices. No Hardware is a Monitor. Conclusion:
I. All Computers can be Hardwares.
II. Some Peripherals are not Monitors.
III. All Monitors can be Devices.
IV. No Computer is a Device. 

Only Peripheral are Computer → All Computer are Peripheral and Computer cannot have positive relation with anyone. Hence conclusion I does not follow but conclusion IV follows. Some Hardwares are Peripherals (I) → Conversion → Some Peripherals are Hardwares (I) + No Hardware is a Monitor (E) → Some Peripherals are not Monitors (O) . Hence conclusion II follows. Some Hardwares are Devices (I) → Conversion → Some Devices are Hardwares (I) + No Hardware is a Monitor (E) → Some Devices are not Monitors (O) → Probable conclusion →  All Monitors can be Devices (A). Hence conclusion III follows.