Make sure there is adequate ventilation .... space around the switch,
Make sure the temperature is not too hot.
Make sure the power is stable. If the switch is plugged into a UPS, try it directly into an outlet; UPS batteries do go flat after a while. You can try another UPS as well. Make sure the UPS is rated to support the power draw of the switch.
The power supply of the switch can be flaky. If you've eliminated the power and environment, chances are good the switch's power supply is defective. You'll need to RMA the switch.
There is a chance (as previously mentioned) that there's something like a memory leak / code bug. If by "restarted repeatedly" you mean that it is in a constant boot cycle and never comes up, then you (almost certainly) have corrupt IOS and it needs to be reloaded.
If by "restarted repeatedly" you mean every hour or two, every day or two ... something like that, then we're back to bad power, bad environment, or buggy code / memory leak.
In the future, it would be a great help if you also posted the code rev of the device you're asking about, as well as any troubleshooting you may have already done.
Good Luck
Scott
