Can i pour a new top layer of cement on an existing uneven slab with huge cracks.?

you can. The new slab will need to be at least six inches thick with rebar. The concrete with fiberglass would add extra strength. A contractor poured my garage floor 14x21 with only six concrete posts into sub grade about 2 feet in diameter using this method and it is fine after 15 years.

Not enough space here to describe the entire process but the big cracks are a major problem because they will continue to move. The movement will cause the cracks to show up again on the in the new layer of concrete.

You current slab lacks sufficient reinforcing and inadequate grade beams. Anything you put on top of it will crack. Just cover it with some sheet vinyl flooring and forget about it, and it will be cheaper than anything you do to the existing floor. If your neighbors do not have similar problems, probably your house contractor dug a hole and threw his old construction material in it.

if you want to do this correctly then hire a concrete tech and get it thick enough to hold the rebar and ''' hardware concrete cloth = squares of wire """" that will keep your new topper from freezing and being just as bad as what you have now .... the depth od the new concrete will be determined by the extreme cold in your location ... hire someone to supervise, direct, advise, or do the work .....

You could pour self-leveling concrete on top of existing concrete. But the crack is just going to show up again, and rather quickly I'd bet. You are probably better off cutting along the cracks, chip out a section, then pour in fresh concrete to fill it.

From the looks of things, the slab may not have had any rebar installed to help keep it together.

An expert in my area had this to say about slabs: "...When the soil under the slab moves and sinks, it puts pressure on the concrete floor. That can be a big deal. Depending on the width of the crack, and if it’s growing or not, you may need to investigate. Another indicator of a potentially serious problem is if one side of the crack is higher or lower than the other. What looks severe to some might really be minor, but you need to have a professional inspect the problem in person..." (Mike Holmes, Holmes on Homes TV show)

That's a slab which was improperly engineered. If you pour over it the new cement will soon crack as it is controlled by the bottom slab. Your soil is obviously unstable and the slab should have had wide deep beams incorporated to prevent shifting.

I'm a cheap bastard, so I'd just keep patching it until it started to become REALLY unacceptable.

at the least isolate the two layers from each other , shifting of the lower layer is likely to break the new work, is that outside, replace it, if it is inside just leave the wall supports and remove and re-pour the floor!