not recovering from sleep

[syrenab]

I have a T22.
All of a sudden when I click the Fn button to return from Sleep it turns the computer OFF.
Then I cannot restart. The on/off key causes the light to flash, but nothing happens.
After about 3 hours, I can restart normally, as if nothing had happened, and then Thinpad works perfectly, until the next time I go into sleep mode.
This is not a heat problem, the Thinkpad is cool.
It is not a battery problem, the battery is almost fully charged.
Any suggestions?
B