Way 1 Maybe the SSD is not installed properly, try to reinstall the SSD hard drive. If we reinstall the SSD, we can enter the BIOS, but can't see the SSD, it may be a SSD hardware problem, we can put it on other computers to test it. It may also be a problem with the BIOS, we need to update the BIOS.
Way 2 Does the Windows 7 support UEFI or MBR boot mode? If Windows 7 support UEFI boot mode.
We can try the following way:
- Put HDD back to Lenovo S400 Touch.
- Go to BIOS, turn off Secure Boot.
- Then it will display legacy boot and UEFI boot.
- Turn off the laptop, replace Lenovo S400 Touch HDD (Windows 10) with a new SSD (Windows 7).
- Try to reboot, view if we can boot successfully.
![enter image description here](https://cdn.statically.io/img/i.sstatic.net/o2w57.jpg)
Way 3 If the Windows 7 supports MBR boot mode, we do not need to try the way 2. If we can see SSD in BIOS after reinstalling the SSD hard drive (click F1 key), we can try to fix the boot.
Way 4 Reinstall the windows 7 operating system, if it supports UEFI boot mode, we can refer the article: How to install Windows 10 from USB with UEFI support
How to Upgrade Your Laptop’s Hard Drive to an SSD