my mac computer keep restarting on the apple logo what to do?

Please refer to If your Mac starts up to an Apple logo or progress bar - Apple SupportI

My initial thoughts are that it has likely suffered a hardware failure, I strongly recommend that you make an appointment with your local Apple Authorized Service Provider to have the computer professionally diagnosed and repaired. However of course please click the above link and follow Apple's advice.

If the iMac is a 2015 or older please take it to an independent Apple Authorized Service Provider, a 2015 iMac is now considered vintage and Apple Stores will not work on them, however independent AASPs may.