HELP with access to my school's website? Need it ASAP!!

So about two or so months ago my school's webpage was fully functional. I could use everything no problem. Apparently the site got hacked. I was able to contact the web developer of the site and we emailed back and forth from the link i have to their email on my phone.We tried to resolve the issue numerous times as they had supposedly switched servers or something of that nature to add security. The site was and still is sketchy at best on my phone but i can easily bypass the security warning and access the page now. The problem I am having is with my desktop computer. Ever since this issue I cannot access the website for the life of me-- except for the registration part of the site that i have bookmarked. I have tried all of the web developer's theories and nothing has worked. She even tried to send me a link to their I.P. address to access it. Her final email to me was that if i had or had ever had AVAST anti-virus installed on my computer and if so that it was probably the case or case of old remnants of it causing the issue. I searched and found them but could not delete them apparently i do not have permission to do so. I have even tried avast's uninstall app. I have not had this anti virus on my computer in over 2 years and had no issue prior to this "hacking". Also one of the last things she mentioned to me before she quit replying had something to do with her telling me that Avast changes my computer's DNS settings and their servers haven't been updated with the school's new Website IP address and the servers are still trying to direct me to their old IP address is why i'm not able to reach the site anymore and get an error connection timed out result. She instructs me to change my DNS settings and the problem should resolve. I asked how i would go about that and she has not responded since and its been about a month. I'm not fully sure of what i was being told or not but i am on a mission to get this up and running before the new semester starts. I have lastly tried CCleaner as well as downloading IE explorer and Firefox in desperation (chrome user). I am the only one of my friends who attend the school that are experiencing this issue. Is there anything at all possible besides rebooting the computer from the beginning that i can do? Any advice is greatly appreciated. Thank you for your time.
-Jessica