BOOTMGR message is continuously popping on startup
If you see this error whenever you start your laptop, check if you have a USB flash drive attached on one of the USB ports of your computer. Most of the time, it is the usual cause of booting problems. The reason why this happens is that, when you start the computer and a USB flash drive is connected, instead of the computer booting on the system drive, it will divert the booting to the USB flash drive.
If this happens, you will see an error on your screen as if there is a problem in your operating system. But in case you don’t have a USB flash drive inserted on your computer and you still have this problem whenever you start your machine, try repairing it using the Windows Recovery Environment or WinRE.
To begin, insert the Windows installation CD then restart the computer. Boot your computer using the CD then when you see “Press any key to boot from CD or DVD” on your screen, press any key. Follow the instructions then click Next. On the next screen, click “Repair your computer”.
In System Recovery Options dialog box, select drive C or the drive where Windows is installed then click Next. In System Recovery Options dialog box, click “Repair your computer”. Select the operating system you want to repair and then click Next. In System Recovery Options dialog box, click Startup Repair.