I already have that but it works for www.website.com/productA it doesn't help with www.website.com  and I see AbanteCart cart logo by default so I just want to know where is it coming form

Try this
@media only screen and (max-width: 500px) {    #banner_slides {        display:none!important;    }}

I think it is overwritten somewhere . can you see all the CSS applied to this ID.
Can you share the url?

Your apache is giving error because you are using port 80 that is already been used by other services
To resolve this error you need to use available port
click on config button next to stop, admin and before log for apache in xampp control panel there you will see 3 files with apache prefix open each of them one by one press ctrl + f and look for number 80 replace them with any other available port for example 8081
do this for all apache files then restart apache. This will solve your apache error

once it starts then you need to change your url from localhost:80 to localhost:8081

Installing abantecart through XAMPP is really simple but you need to have some basic knowledge but don't worry thats what we are here for.
Try it and then let me know
P.S I am also XAMPP user and abanteCart work perfectly fine with it

If you want your navbar to stay on-top always then modify the following line:
/storefront/view/default/template/common/header.tpl line#2 <div class="headerstrip navbar navbar-inverse" role="navigation"> to <div class="headerstrip navbar navbar-inverse navbar-fixed-top" role="navigation">

Hi is there a way I can ask customers to enter their email/phone number to get notified when I will have a product back in stock?

Yes, I suggest to clear cache after every database edit and also clear browser cache

Go to your admin panel System->localization->language Definition   
Or you can directly search the word in search box which is at the  top of your admin panel