At this link you can find instructions on how to find the serial number of your Mac and how to check the manufacturer warranty.

Note: If you have purchased an extended warranty from DQ Solutions AG (DQ CarePlan) or your Mac is still within the 2 year statutory warranty period, this will not show up in the Apple warranty check.
Check your purchase receipt for the date of purchase and if you have a DQ CarePlan that is still valid. (Contact DQ-Solutions if you no longer have the purchase receipt).

More information about the warranty for Apple devices can be found here.

If your Mac won't turn on or can't complete the startup process, try the solutions described here:

• My Mac won't turn on or boot

Software updates from the laptop manufacturer are important for the smooth operation and security of your laptop. 

• Keep your Mac up to date

Apple usually supports the three latest macOS versions, so if possible do not use an older macOS and upgrade to a newer macOS operating system version at least every 3 years.
Since sometimes there are still problems with the newest macOS version and it sometimes takes some time for third party software to release fully compatible versions, we recommend to use the second newest macOS version.

• Update MacOS

Apple Diagnostics and Apple Hardware Test are tools that help you analyze and detect problems with your computer's internal hardware components, such as the motherboard, memory, and wireless communication components.  

If a Mac is experiencing problems related to settings stored in non-volatile RAM, resetting NVRAM or PRAM can help. (This can solve problems with volume, audio output, screen resolution, startup volume selection, time zone setting, etc.). 

On our Apple manufacturer support page you find all information about the warranty and how to open a warranty claim.

If you have any difficulties, we will be happy to assist you. Just send us an email.

Data loss can happen at any time and for various reasons. We recommend that you back up your data regularly.

Apple's Time Machine, your Mac's built-in backup feature, lets you back up all your files - including apps, music, photos, email, documents, and system files. Files backed up this way can be restored from the backup if the original files were deleted from the Mac or if your Mac's drive was erased or replaced.

• Backing up a Mac with Time Machine

For more general backup tips, visit the ETH IT Security website: Protect your brainwork.

The utilities in macOS Recovery help you restore from Time Machine, reinstall macOS, get help online, repair or erase a hard disk, and more.

• Information about macOS Restore: reinstall macOS from macOS Recovery
• Information on how to restore macOS:
  • Intel based Macs
  • Mac with Apple chips

With bootable installation media you can reinstall macOS if e.g. the macOS recovery is not available: 

• Create bootable installation media

If you're having trouble accessing your Apple ID, these steps may help.