HP Pavilion A 1518 IN, Media Centre PC, Sr No. INi 6240 Mq6 — Booting and other Misc Problems

I have HP Pavallion a 1518 in, Media Centre PC, Sr no.INI 6240 MQ6. There is booting problem in the PC. When we switch on the PC it boots again and again automatically. DVD writer/reader is not working properly. It is producing abnormal sound. Speakers are not working properly, some times it works, sometimes dont work. Processing speed is very slow. These problems are persisting from las 6 months. HP dealer is also not serious about the problem. Ungent action is requested.