When a PowerPoint show is converted to a web presentation, it is not compatible with a screen reader.
Here are some suggestions that will help make your show more available.
"People who use screen readers will need to have the slides in HTML format in order to access them. This is the only format that can be considered reliably accessible to the various brands of screen readers on the market. Some screen readers can read PowerPoint slides on the Web to some degree, but not well enough to be considered truly accessible.
As for the other disability categories, those who are deaf will be able to access the slides without any problems, unless there is embedded multimedia. In such cases, captions and/or transcripts will be necessary. Those with motor disabilities will have no special difficulties. Even those who cannot use a mouse will be fine, since the slides are keyboard-accessible. Those with cognitive disabilities will not have any particular difficulties, although text-only presentations may be difficult in some cases. "