ANSWER - As with any talent or skill the desire and ability to practise witchcraft will peak and wane. This may be on a cycilic basis (some witches feel their power more at various times of the year), it may be a relation to a life event that creates a mental state of mind which is not suited to practise of the craft or it may simply be that life gets in the way.
It is also important to note that as we travel through the different aging periods of our lives our abilities change. Many children, for example, have the ability to interact with spirits but in most cases this ceases before adolescence or adulthood.
As a witch goes through his/her life there are periods of time that are less suited to the craft that others. Feeling miserable and depressed will certainly have an impact on your ability. If you are channelling all your mental strength into functioning then it is no surprise you do not have enough left over to fuel your other abilities. I’d suggest not pushing it, we all need to take a break sometimes.
The counter position to this however is you use your craft to get yourself out of this low ebb. Rather than waiting for your specific powers to return get yourself into a good head space spiritually. Regular meditation, interaction with nature, returning to good basic practises like grounding and shielding will help you become more focused and create a better head space for the return of your abilities.
A witch’s power could theoretically be sealed by another witch. It isn’t something I have personally come across but I can see no reason why a more experienced witch would not be able to cast a binding that would limit the efficacy of another. However I think this unlikely. A witch would only cast such a spell if the intended individual was a threat to him/her and it follows that if the target was a threat they would either have too more power for the binding spell t work or it would inflame further animosity between the witches.
As with most things in life the simplest explanation is probably the best. You are working through a low ebb and will get back your abilities when you have worked through this period in your life and also taken steps to improve your spiritual strength.