If it's not acquiring satellites there's probably a problem with the internal battery.... how old is the unit?.... Your first call should be to Garmin customer service.... I've had mixed success with them over the years... first time with my Garmin 45 (the white one) I sent them the unit and they returned it completely refurbished within the week, no charge. The next time it went down, a year later, they wanted $100 to do the same thing. NO WAY... I went out and bought a Garmin 76 that has performend flawlessly for nine years.
The problem I had was exactly the same that you described. Good Luck....... you must call Garmin though...