remove malware from website (not wordpress)

I have built 2 websites for a client and suddenly they seem to be infected with malware or ads. They usually run perfectly and i dont notice anything wrong - however they are a little slow to load sometimes. When i first go to the websites in the bottom corner i see "waiting for .." and some dodgy sounding domains such as "[login to view URL]" and sometimes many others. See the image attached a weird white bar has appeared with failed images that link to an ad website, must be related. (doesn't always appear). Do not try and find or contact me through the website, it is not my website i just built it for a client. Please start your proposal with "bitcoin" to be considered and advise on how you would try and remove the issue or what it could be, website was built in dreamweaver. Thank you steven