Starter not rising

Hello, I'm after some advice.

I have recently activated some Dyhydrated starter that I have. The first week it became really active and was rising and falling at a good rate, but since then it has really become really dormant.

I have tried feeding it twice a day and putting it in a warmer place but it it is still not rising at all.

There are a few bubbles on the surface but that seems to be it.

Any ideas or help would be really helpful. 
 

Cheers, Keefy