I lose my maximum site PR this month. Some of my site was PR 2, it is now PR1. Besides, I lose my Valid PR 7 t 0! I can't understand why. Do you know anything about it?
I think there may be something wrong activity you did which was unethical in the eyes of google or some virus issue or something else. But there is some major PR updates in which google told that they will calculate PR only on the quality of backlinks and content of web page.
As you said that your main PR7 went to 0 that's why another blog lose too. You will need to build it back.
Yes I couldn't but agree you have done something that Google consider unethical and you have well and truly paid the price. You will have to fix the problem and start again