Question mark inside black square replacing symbols?

Ok, I see what you mean, in this case it's not characters, it's the encoding like sapta stated, if switching fixed that one but made others worse, then it just means that whoever set up that post decided to use a character et different from everyone else...I wouldn't worry about it as it's nothing wrong with your pc, just someone trying to be different. But, in most cases it is usually a font missing from your pc. Try to do a search and find out if you are missing any default fonts