You was UPS. Served it to you faithfully pretty long, eg, several years. Here suddenly it fails. How to Apply? In general, about this problem you learn from this article.
If you still decided their hands do fix, then first need get information how practice repair UPS. For it one may use finder, or look archive binder magazines like "Junior technician", or search response this question on appropriate community.
I hope you do not vain spent efforts and this article may help you solve this problem. The next time I will write how fix a motor or suspension.