Can't change Skin

Hello forum...
First, I'd like to apologise, just in case my question can be answered by reading some FAQ article. If so, please re-direct me an lock the topic
My forum uses the default Prosilver skin by forumgreek, with some minor customisations. Specifically there's some HTML headers and occasionally we use javascript, for cosmetic purpose...Falling snow in christmass period for instance...

I tried to install a new skin via the Hitskin page, but the page itself seems to be unresponsive... I tried another URL, from another forum and it worked like a charm, transforming everything in their case, from headers to widgets. So, I suspect there's something in my case creating conflict, but I can't figure exactly what.

Tried disabling some of my custom code, but no change... There's a lot of people using the forum 24/7, so I wouldn't like to mess with everything, changing to "vanilla" Prosilver, loosing the images, icons and stuff...

All the above lead to a couple of questions I wanna ask...

1) Do you think my problem has anything to do with the custom HTML/Javascript used on the home page (and what else could it be)?
2) Considering there's no other way, but to disable everything, set back to the default skin and then try again with a new one... Is there a guaranteed way of saving my current state of the forum, just in case I make a mess experimenting? Does Export/Import serve this cause?

Thanks for your time and your answers and "sorry for the bad language" (not a native speaker)
Cheers from Greece

You will need to save your customized CSS stylesheet and template modifications.  When installing a new theme, they are erased.  Codes on your forum should not effect installing a new theme.

When installing a new skin you must be logged in to your forum and the best way to install the skin is to do it by Hitskin.com.

you must be the founder of the forum to install the skin to your forum.

Thanks for responding...

I'm not the founder. The founder is kind of "missing"... The admin-team runs the forum for the past 3 years or so... Aren't administration rights enough for the change of a skin? All of the admins can change between the given skins on the control panel... But we can't do it through the hitskin site.

Are you pressing the review button or install button? If you are pressing the review button, are you pressing the install theme link?

Neither of these options work...

Try and install it from Hitskin.com but i think its fonder set so only founders can make the change