Bonsai are proper tree's with the exception, when grown in the manner to form the bonsai shape and habit of growth, then they have to be cared for and their treatment must replicate the tree would require when growing naturally in it's natural habitat.
The difference for growing the same specimen as a normal growing tree and one grown as a very strict set of rules to form the tree into a miniature shaped and wired form, is very time consuming, exacting in treatment, careful pruning of top growth AND roots.
That's JUST to get the proper form, then you have to mimic the growing temps, shade/ light etc and make sure the roots are kept alive yet short, small enough to keep them withing the confined's of a very small-shallow (preferably china container.
you have to wire the top branches into the shape suitable to replicate the natural growing shape, for instance IF you want the tree to look like it has naturally grown on a cliff face and been battered with wind from the see or one direction, then you have to begin wiring the branches to replicate the growth forming in the direction of the wind, you would be required to snip the branches also to form the shape of such.
You need to emptu the root end out the pot, wash ALL the soil out, proon any roots too long and too hard wooded, A small pair of nail cutters would normally do this OK.
Use fresh soil with added feed, lay a small layer on the bottom of the container, spread out the roots onto this soil, add handful of soil mix, TAP / Shake the container to allow the soil to drop evenly in between the roots, use fingers to gently fill the spaces so there are no air pockets, once you have securely filled the roots into the soil / container, you may have to help secure the small tree upright by using Florist wire strapped over the pot holding the roots in place and the plant upright.
Water sparingly, remember in natural environment the tree roots would spread out in search of water, your Bosai cant to that so it's up to you to get the watering regime in place, same with sun /strong light, ask where you tree would grow in it's natural habitat and try replicate that.
Smaller trees would normally grow in dappled shade at the edge of woodlands or sheltered from really hot sun by the canopy of taller trees.
I would say your plant is as close to death as can be, it's been allowed to dry out for too long between watering's, too much soil in the pot around the roots drowning them after each watering, too little water between a good wetting and and then left unprotected from your heated spot to be able to cope with such fluctuation in differing temps / light and I would say in need of a more shaded area, try stick fingers into the soil between watering and if dry, give water, if wet leave off the water till needed, Make sure there is drainage holes in any containers you use to allow any excess to drain quick enough to prevent the roots sitting way too long in wet soil.
These plants really are very tricky to grow well BUT you do get lots of fun when you get used to how to treat them. Please dont give up just yet, maybe a different type of tree would suilt your temp etc better and easier.
Go to the book store or local library as there are books there for beginners bonsai,
Kindest regards
WeeNel.
