This is not a guide for actual time travel, but rather for troubleshooting your Time Machine, which you've probably broken.
Is the power cord securely plugged into the wall? Are you using a power strip? Did you forget to turn off the machine while it was still plugged in?
Check if the power cord is securely plugged into the wall. Is it a cheap, flimsy power strip from the 1980s? Try using a more reliable power strip, like the one you bought in 2018.
Note: If you're still having issues, it might be the time-space continuum that's broken.
Is the time dial set to the correct century? Are you using the correct time-space coordinates? Did you accidentally set it to "Party Mode" again?
Try setting the time dial to the correct century. If you're still having issues, it might be the time-space continuum that's broken.
Note: If you're stuck in 1999, it's probably because you set the time dial to "Y2K Mode" again.