Windows 10: cannot locate operating system

My dell 7500 has windows 7(C: drive) and windows 10(F: drive) installed on the single internal HDD. It also has three USB disks used only for data. When I boot I get a message saying that an operating system cannot be found and I should try unplugging my USB drives and then reboot. When I unplug the USB drives and re boot, it finds the windows systems and finishes the boot process with no trouble.
Checking the BIOS shows only the CD-Rom drive and the three USB drives are listed in the boot order and the drive listing. I then deactivated the "boot from USB drives" item in my BIOS and then the computer boots fine.
Also, I have been experimenting with Ubuntu on a USB pen drive but have removed it. I suspect that there are some parts of grub hanging around.

Why can't the bios find my internal HDD which contains the two Windows systems?

:)

 

cannot locate system reserved partition on Disk Management

This Windows 10 upgrade error is usually caused by insufficient space on the System Reserved partition. When you install Windows to a partitioned MBR disk, Windows will create an additional partition without drive letter labeled as System Reserved, which
stores important boot files and normally locates before the system partition (often known as C: drive). On Windows 7, it often takes 100MB disk space, 350MB on Windows 8, and 500MB on Windows 10. Since upgrading to Windows 10 needs more space on the System
Reserved partition, Windows 10 will not upgrade unless it detects that the System Reserved partition has enough space. If you fresh install Windows 10 to a specific partition, you won't receive this error. By the way, the System Reserved partition first appearance
was on Windows 7, so you won't have this error on previous versions of Windows.

To solve this problem of being unable to update System Reserved partition, you can increase the size of System Reserved partition using third party free partition software like AOMEI Partition Assistant Standard, which can manage your disks and partitions
without data loss.

For detailed solution, see this article: Fix "We Couldn’t Update the System Reserved Partition" Error

 

cannot locate system reserved partition on Disk Management

Your System Reserved partition might be too small and you need to resize it to about 600 Mbs. See instructions how.

Press Windows key + R

Type: diskmgmt.msc

Hit Enter

Click the system drive to view the size.

Resolution:

Create a recovery drive:

How to: Create a Recovery Drive for reinstalling Windows 10

http://answers.microsoft.com/en-us/windows/wiki...

Download Ease us partition manager and resize it to 600 MBs

http://www.easeus.com/partition-manager/epm-fre...

For this example, I will be using Ease us partition manager:

After installing Easeus partition manager, launch the program.

Select the system partition where Windows is installed.

Click Resize/Move button on the toolbar

Under Decide size and position, use the slider then drag to the left until a desired amount of space is allocated - 600 MBs. Look in the Unallocated Space Before: field to see how much. Once that is done, release.

You will now see an unallocated amount of disk space created. Click OK

Click Apply and OK to confirm changes. Your computer will be restarted to apply the changes.

After restart, log in and launch Disk Management – press Windows key + R > type:diskmgmt.msc then hit Enter on your keyboard.

Select the System Reserverd partition, right click it then click Extend Volume

Select the Unallocated space we created earlier, click Next then click Finish.

You should now have a large enough System Reserved partition to accommodate Windows 10 setup.

Important note: Backup your computer:

When making significant changes to your computer such as updating the operating system, you should always backup. See links to resources about backing up by clicking the link

How to: Create a system image in Windows 10

http://answers.microsoft.com/en-us/windows/wiki...

 

You have to get your BIOS boot sequence right. CD ROM as first and then the HDD from which you want to boot. Make sure it contains the bootmgr.