Luego de previsualizar un rato mi pc se reinicia

I assume, that the computer isn't restarting, but crashing. It's a new fashion to hide any blue screen or fatal error message in this scenario and just restart after the crash.

The first thing you should check is the error protocol of windows. Right click on start icon and go to the event log. Switch to admin view and search of the time, the computer crashed. Have a look for kernel power events and what was happening around those events.

Is it a desktop pc or laptop? You laptop might just overheat and get unstable. The same can happen to a desktop if cooling is not powerful enough. Get HWInfo tool to monitor temperatures.

How much RAM did you allocate to AE? Windows alone needs around 4GB to run.

You can install prime95 and make a stress test to check cooling, RAM, temperature and power supply. Get furmark and stress test your GPU. For ultimate stress, do both tests at the same time. Before running any of those tests, make sure to know where to stop the stress test. You computer might get very hot. Until a certain temperature, there is no need to go further to know something is wrong.

Regarding the preview length: I'm not sure if you cannot render previews for longer then a minute (and now up to 10 minutes), or if you cannot playback your work for longer than a minute. Those a different situations. If you render the preview and after one minute the computer crashes, or restarts, something is odd and it might be hardware related.

If you render the preview and the rendering stopps after one minute and playback starts, this is just normal behaviour. AE is rendering straight to the RAM and sooner or later, it is full. So rendering stops and playback starts. Usual you are not previewing minutelong, but just a few seconds of your work.

Regarding your file: since the computer crashed, the project file got corrupted. Open AE and create a new project. Import the broken project file and cross fingers. If it loads, safe it immediately. If it doesn't load, open your latest autosave. It's good practice to make manual backups of the project file on a daily basis, too.

*Martin

luego de reiniciarse, al abrir mi archivo me salio que estaba dañado, estuve trabajando por 2 meses ese proyecto para mi trabajo