what do you mean by "losing picture"
1. Is it pixel-ated? (bad quality)
2. Is it filled with artifacts? (random colored bars/squares)
3. Is it flat out not there as in a blank screen?
If it's 1. Its probably because you TV is capable of HD and anything less looks poor because the TV has to fill area with less data. Meaning your TV can fill 1000 squares but your signal only has 480 squares worth of data so it makes the squares fatter.
If it's 2. It's likely your providers box. You should has for a tech to come out and take a look. It may just be temporaty, as in they messed something up on their end before they pushed the signal out to your box. It can also mean a bad line. The line from your house to the pole or even and entire stretch of line along the pole could be bad. What your seeing is a loss of data and the TV or Box filling it in.
If it's 3. It could be the TV or the Box. It's hard to say which. It could also be a loose connection between the two or between the Box and the wall. Best to check the connections before calling your cable provider.