How can I get through to my brother?

My brother is a very sweet and loving 5 year old. He interacts with other kids very well, but when it's just me it's a different story. Our mom works very long hours and is rarely home so I have to keep the house intact and watch over my brother. With an eleven year age gap we get along very well, but when it comes time to leave the park, help me put away his toys,  turn off the T.V./ video games, he becomes very angry. He hits, screams, throws objects and causes physical harm to himself. He has been diagnosed with ADD, ADHD, Autisim, severe sleep disorder, and is Bipolar. I know he can not always control himself and acts upon his impulses, but I don't know how to get through to him. I've tried letting him go to his room and cry it out, sitting in the corner, giving him a little extra time to do fun things before helping out, trying to reason or ask him how he's feeling and why he's doing it. So far nothings worked for me. Are any of you in the same situation or been in the past? And if so what's worked for you?

[margypops]

Kindness will work, there must be a reason he is behaving this way, what happens prior to a tantrum ,it is really up to your  mom to find out why he is doing it ,he sounds upset, so speak to your mom and ask her to be around more, she is the adult its not fair on you to be looking after a 5 year old all the time, what happens when you are at school? Perhaps you can be flexible on how you get him to leave the park, put his toys away turn off the TV   If he is on Meds they sometimes have an effect on his emotions, all the more reason your Mum should take control and not leave it to you .Good Luck