On pushing in the start button, it just cuts out immediately, within a fraction of a second.
" they tell me the software is corrupted badly. "
that does not sound right to me. If it were corrupted software it should at least attempt to POST [ thats were the writing flashes on the screen proir to loading windows]
If the computer shows no writing on the screen and it shuts down almost immediately, it sounds as if you have either something loose or that something has gone. In these situations it's usually the psu [ power supply unit] that fails.
Try telling us something about the computer. was it shop bought or home made. has it got a makers name and model number. Do you know what operating system it is using [e.g. xp or vista ].Any thing that may help us to help you.