Could be this:
Miyano311 wrote:Maybe it just goes slowly. I experience the same thing every time theres an update.
Try waiting for a few minutes and hope it will load up.
but a quick search as a non-Onigiri related problem suggests things like disabling your antivirus or running it as an administrator. There are other suggestions too so maybe it's worth looking into the problem as a program rather than onigiri problem i.e. program won't open but visible in the task manager.