There are a few options for you...
1. Check to see under what kind of conditions the GPS loses it's signal. If there are tall buildings, is a cloudy day etc or even the position of the GPS in the car (does it have a clear sight of view of the sky)... In the latter case, you could change the position of the GPS where it gets a clear view of the sky. For Cloudy days, better have a map ready or preplan the route using mapquest/googlemaps, as nuvi 200 series is especially notorious for these type of situations. For tall building problems, what I do is (c330, not nuvi), just tap the route displayed on the top before the signal gets lost and memorize the next few upcoming turns. Or avoid downtown (where those huge skyscrapers are)
2. If you have enabled WAAS setting in the settings menu (it should be somewhere under "GPS mode", disbale/uncheck it and use the normal GPS mode. WAAS may provide you a more accurate position, but at the expense of some avaialble satellites.
3. Or your GPS may have a genuine problem, then your only recourse is to call Garmin and talk to them. Here's the contact info:
Support North America
(for all Garmin products except Apollo aircraft)
Monday - Friday
8 a.m. - 7 p.m.
Central time (closed holidays)
Email Product Support: TechSupp@garmin.com
Product Support Phone
1-866-429-9296 (Canada) or (913) 397-8200
Good Luck. Personally I would avoid the 200 series and go with the 3xx, 6xx or even better the 7xx series (if you need all the bells & whistles)