Feed dogs on my machine wont rise above plate

If the fabric is not feeding, the feed dogs are probably not operating properly. Check that they have not been dropped below the needle plate (which is done when darning or free motion quilting). In this setting, the feed dogs never rise above the needle plate to grab and pull the fabric.

The other issue could be that the feed dogs are defective or perhaps seized.

Since you did not provide a model, I can provide only this assistance. It would be helpful to locate (search for make model manual) for your machine.

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Consult the owner's manual. There should be instructions for how to darn with your machine. It would require either the feature that lowers/raises the feed dogs or a cover plate that attaches over the feed dogs.

If your machine came with the cover plate accessory, and the feed dogs are not rising to feed the fabric, then I suspect the machine has not been cleaned & oiled in quite some time and perhaps the feed dogs have seized. When you run the machine (remove the needle and presser foot), watch if the feed dogs actually drop below the needle plate, move toward the front of the machine, then rise above the needle plate and move toward the back of the machine. This is a repetitive motion that actually pulls the fabric through the machine. If this is not happening with your machine, it needs service.
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Singer Stylist 776 Manual Page 8

check the position of the forward/ reverse setting
near the middle will not advance the material

take it in for a service

Check that the stitch length is set to make ~10 stitches per inch. This stitch is long enough to actually move the fabric. If the stitch length is set too short, the fabric will stay barely move and the needle will stitch almost in place.

Check that the feed dogs have not been dropped for darning or free motion quilting. In this position, they do not rise and are, therefore, unable to contact the fabric to pull it through the machine.

With the presser foot raised and using no fabric, hand rotate the handwheel and watch if the feed dogs actually drop down below the needle plate, move toward the front of the machine, then rise above the needle plate, and move toward the back of the machine. If the feed dogs are moving in this manner, then they are functioning properly.

Is there lint or gunk stuck in the feed dogs? This will restrict the ability of the feed dogs to grip the fabric.

Are the feed dogs worn? Are the little teeth worn so there are no sharp points?

What type fabric are you using? If it is very light-weight or slick fabric, the feed dogs will have a difficult time gripping the fabric. Most machines have a presser foot pressure adjustment so that more pressure is applied between the presser foot and the feed dogs. Consult your Owner's Manual. The adjustment is usually a dial either on the left side of the machine, on the front of the machine located above the needle bar, or on vintage machines it is usually a skrew located under the top lid above the needle bar.

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Tension generally does not affect the feed unless it is way too tight. Most reasons for fabric not advancing under the presser foot is that the feed dogs have been dropped for darning. If the feed dogs are operating properly, as the handwheel turns the feed dogs should rise above the plate, move toward the back of the machine pulling the fabric, drop down, come forward and rise again.

The other possibility is that the presser foot pressure has been released so the presser foot is not holding the fabric down on the feed dogs. Some machines have a spring-loaded knob on the top of the machine, a dial, or something to adjust the amount of pressure the foot applies. Consult your owner's manual.

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With the straight stitch set to zero the feed dogs should be down. To use a different number will make the feed dogs rise above the plate.

Look at the feed dogs to see if they are rising above the needle plate at least 1 mm. If not rising lint may have felted between the feed dogs and the needle plate. It could also be the feed dogs have been lowered, or the height has slipped. If the feed dogs are above the needle plate turn the hand wheel and see if they are moving from the front of the machine to the back. If not it is a length adjustment. If this is normal the pressure on the fabric may be too low. Another problem may be the timing of the feed dogs. The feed dogs should rise above the needle plate when the needle leaves the fabric and descend when the needle comes down into the fabric. This requires an expert to fix.

when the feed dogs are in the up position the sewing machine
will sew
but when the feed dogs are down postion it will darn
try the feed dog lever again if you can move the feed dog lever and
the feed dogs respond going up and down then you know that
the feed dogs are working and are not broke
but if they do not respond then they need to be checked to see what's
wrong with them

Check whether the feed dogs are coming above the stitch-plate at their maximum height. They should be about 1mm above the stitch plate when driving the material under the foot. I assume, by the way, that you haven't got the feed-dog drop button pushed-in at the handwheel end !!! If the feed-dogs are lower than 1mm, or not above the stitch-plate, the dog cam cam-foller will need adjustment. You have to remove the front cover to get at this and it should be done with a special gauge, so really its a service agent job, however, for what its worth;
With the front cover removed to gain access to the free-arm mechanism, look to the right of the hook race and on the end of the bottom drive shaft there are two black plastic cams . The right-hand one regulates the movement of the dogs front-to-back in association with the stitch-length stepper-motor, which drives the upper shaft in the free-arm. The left-hand cam regulates the up-down movement of the dogs and the cam follower (a piece of right-angled plated metal) has to be adjusted to determine the maximum height of the dogs aboe the stitch plate. The cam follower rubs against the top edge of the dog cam. There should be a small spring that pulls the cam follower down onto the cam at the front - if that's missing, the feed-dogs probably wont move quite correctly. To adjust the dog height, turn the hand-wheel until the feed-dogs are at their maximum height, unscrew the small screw in the left-hand side of the cam follower a couple of turns (dont, for goodness-sake, take it out !) - the feed-dogs should then pop-up above the stitch-plate. You now have a problem without the proper gauge ! You need to gently push the dogs back down against spring pressure until they are the correct height above the stitch-plate and tighten the screw on the cam follower. This should, at least, get over the problem - it wont be exactly right without the gauge and there is another adjustment that should be done to ensure the front and back of the dogs are at slightly different heights, but it should be good enough without this.

Good Luck !!!

What on earth are you trying to do? Feed dogs move the fabric and are doing what they are supposed to do. Are you trying to darn? Embroider? Normally there is a plastic plate that you put over the feed dogs to do that or there is a lever to lower them. I could not find a manual for your machine so I can't tell if you have either of those.