Cutting 45's on my Dewalt 744

Distinti gi? check in internet forum the online manuale?

the slide can be angled by the degree plate where the timber sits
the blade can be angled by the degree plate on the arm that mounts the saw
so you can get a 45 degree to the timber length and a 45 degree angle cut to that angle to give you a corner mitre cut

from your last post this information was missing
when cutting at an angle the cut depth is always reduced and the 5" board is too thick
to do what you want the saw will have to be 10" or bigger because when cutting at an angle you are cutting a hypotenuse which is the longest dimension of a triangle
so if the saw cuts to a depth of 5" at right angles the angle cut will be longer because of the triangle effect

Did you check to see if the saw has a locking nut on the front of the bevel gauge handle? Its possible you just locked it into position and forgot to unlock.

You can solve this with geometry, but it will take forever and your answer will only be approximate (due partly to the limits of accuracy of the scales on your saw). If you are using a table saw, use scraps of wood and trial and error. It takes a while, but you can get a perfect result. If you are using a miter saw, then support your work from underneath at the angle to match your situation, and simply cut at 45 degrees.

Make sure the blade is 90 deg vertical to the saw table. Make sure the indicator is set approprately. Raise the blade just enough to clear the table/base. Place a swanson speed square against the fence and blade. Make sure the indicator is at 90 degrees. Here you might want to tilt the square and check that the complete blade is flush against the sqaure as high up as possible. Lay the square back flat on the table and pull the blade toward you as much as possible. The teeth on the blade should ride against the square extented completely out.

Now set the square against the fence with the 45 degree angle coming away from the table and set the blade on the 45 deg mark on the insicator scale.
The blade should touch the square all the way out fully extented.

Or just experiment with some scrap and check

When you are facing the front of the table saw. Right above the Dewalt logo, there is a hand wheel that if you crank clockwise - it will tilt your table saw blade to the angle shown where the hand wheel is.

Sometimes the knob has to be unscrewed to release it so it can be pushed down or move the table.

The fence may be getting in the way of the arm when you adjust the trunion assembly fully to one side or the other for bevel cutting. Adjusting the fence all the way out away from the trunion assy. should allow full 45deg adjustment. If this is not the case, it could be--even though its only slightly used--that there is sawdust built up enough in the housing to keep the arm from fully adjusting.

While the latch COULD indeed be faulty, it generally should always be tightened/locked so that the trunion assy. is fimly "locked" before cutting as this is designed to keep the saw from shifting mid cut, causing binding, uneven cuts, broken blades, seized bearings, etc.

According to the service manual this saw has a 120VAC single phase 2.5 Hp motor with a 5/8" x 1.5"long arbor. It has a maximum vertical cutting depth of 2 and 15/16". It has a maximum cutting depth at 45 degrees of 2.125" (2 and 1/8") without the lower guards. The maximum cutting depth at 45 degrees with the lower guards in place is 1.625" (1 and 5/8"
The service manuals (approximately 24 megabytes each) are available on line at Dewalt.com After creating an account. Then you should go here:

http://www.dewaltservicenet.com/Products/DocumentView.aspx?productid=18624&typeId=1495&documentId=574

for the manuals.