You will need to take the top off. It is easy: turn the vacuum over and look at the bottom (where you can see the beater bar). There are some deep screw "wells"; these are the screws you need to take out plus the 4 silver looking screws that hold the beater bar plate in place. When you bet those out, there there will be a "notch" at the front, behind the LED light you will have to disengage. Turn the vacuum back over and take the gray top off. You should be able to see the engagement latch that is attached to the handle. This is what opens and allows the flap to shut. It has a spring attached that may have come loose. Good luck.
On page 11 of your manual it talsk about the pre-filter which I think is the one you are talking about, it isn't to come out, so either is pressed in or glued. But if this is less then 1 year old it is under warranty. If it is then take it in and have it repaired, http://www.hoover.com/pdfs/manuals/U9145900.pdf
Copied this from the owners manual off of Hover internet site. Brushrolls are not spinning 1. Belt needs to be changed. 1. Refer to how to change belt. 2. Something is jammed in the brushroll. 2. Remove jammed item from cleaner with unit turned off and unplugged. There is a diagram on page 26 of the owners manual if you have it. I have the same kind of machine. One thing i have found with this type of unit it likes to be clean. So you may have to just take it apart and clean it out. You also could take it to a repair shop to have done if you are not sure how to do it.
Most anything can be fixed if the needed parts are available. You will first need to examine closely to determine where the water is coming from to determine what the problem may be. It is most likely a valve, hose, seal, fitting, tank, etc.
Hoover SteamVac brushes not spinning
This video might help ... it is a related model.
The usual problem with these brushes is that they stop spinning ... not that they will not stay in.
As shown in the video ... they just clip back in by pressing the whole unit in to the housing. The protruding square pin in the middle does need to line up with the housing drive ... or it will not press in. The two alignment posts need to be in the correct position also. The brushes need to be hand wriggled to help alignment so the square peg will enter the square drive hole.
If you are successfully getting the brush unit all the way in ... and it does turn when the unit is turned on ... all I can think of is that the alignment posts have somehow broken...
I recommend blowing it out with a air compressor, some can be washed with water but water can make the fine dust pack into the pores. If it is over a year old it should be replaced as should the other filter or filters depending on your specific model.
Probably a poor design factor that really cant manage the dog hair in the first place !! I always suck a few small coins up and you can hear if they get a unrestricted journey to the dust bag , if you have a blockage you will not hear them clank around as they will get jammed !! this will let you know that your machine is blocked or jammed up causing poor suction !