An operating system wasn't found?

So I was having trouble with my laptop (slow boot and restart etc) and decided to do a reset. I come back and see it's finished removing everything but it also says it couldn't remove some files (not sure which). I restart my laptop and come across a screen saying "An operating system wasn't found. Try disconnecting any drives that don't contain and operating system. Press Ctrl+Alt+Del to restart." I haven't been able to access anything now (apart from the boot settings and setup). I plugged in a hard drive with Windows 10 on it but that had no effect either. My laptop is an Alienware 14 with Windows 10 installed. (Upgraded from Windows 8)
Any help?

dalchina said:

Hi, I would suggest you get this bootable DVD/flash drive:
Windows 10 Recovery Tools - Bootable Rescue Disk - - Windows 10 Forums

That will give you a familiar Windows environment to work in.

Boot your PC from it; download CrystalDiskinfo (free, portable) and run that to check your disk.

Note: viewed from that, your Windows disk/partition may have a different drive letter.

Your initial problems and current ones might be explained by that sort of problem - or could be sthg else. Best check first.

Do you have full backups of your data?

You are also likely to need a bootable Win 10 disk medium, build 1607. It could be a good opportunity to do a clean install if your disk checks out.
Windows 10 ISO Download - Windows 10 Installation Upgrade Tutorials

Thanks for the reply. I'll let you know if that works.
Also, yes, all of my data has been backed up.

dalchina said:

If your disk is ok, you need to decide if you wish to clean install or attempt to fix it.

The first approach would be to simply run Startup repair from you Win 10 bootable medium.

If he is going to boot into Kyhi's recovery tools anyway, a simpler solution would be to run Macrium Reflect included in Kyhi's tools and select the Fix Windows startup problems utility under the restore menu. That has also proven to be much more reliable at fixing Windows boot problems than repairing from a Windows 10 installation drive.