I have less space with me to keep my cabinet case as vertical position so i am thinking to keep it as horizontal posture...will it be safe..without any problem or any loss in the hardware part..help me
Well you could place it horizontal and it would operate normally but my fears would be if it does not say in your computer manual (if its oem) its okay to place it on its side then I would not recommend it. Your optical drive is my main concern since it spins discs at fast speeds and when placed horizontally I am not too sure about the effects. It may malfunction and also your hard drive may wear down quicker if it is not meant to work at different angles.
You can place your machine horizontal (as opposed to vertical like the case was built) without issue providing the motherboard is at the bottom and not hanging upside side down. I would be more worried about airflow than anything, as long as placing the case on it's side does not impede the airflow, then there should be no problems.
Years ago, all desktop machines were horizontal and we still have some around the office that refuse to die. My HTPC is an newer retro style horizontal case and it's runs 24/7/365 for the past several years with no issues.
Also, it makes no difference whether a CD-ROM is vertical or horizontal, again just so long as it is not upside down.