Your school firewall will be blocking it. Please contact your IT department and ask them to whitelist Zendesk.com and ScholarPack.com. This is the main reason the chat box doesn't show, but there may be other causes. Other localised IT settings can prevent this chat box from showing. If whitelisting the above links does not work, please liaise further with your IT team.
Please note that this is only relevant for the ScholarPack chat widget. If you are supported by a third party then you would need to double check with them and your local IT support to see what might be blocking it.