OnePlus Smartphone Stock ROM Flashing Assistance

My OnePlus smartphone is malfunctioning and I am unable to access fastboot mode. I hear the connecting sound and see the USB drivers in device manager for only a couple of seconds before it disconnects and reboots into the system. - The device is a OnePlus smartphone. - The bootloader has been previously unlocked. - I need assistance to flash the stock ROM. The ideal freelancer for this project should have experience with OnePlus devices, stock ROM flashing, and bootloader issues.