Its difficult to accommodate a decent cabinet+Psu within a budget of just 4000.I'd suggest that you keep using your present pc case for the time being and upgrade the psu only.I'm assuming that you have a mid range core 2 duo/pentium Dual core CPU based system and therefore i think an Antec vp 450p PSU(available for Rs 3400 approx) will suffice for your requirements.
It will be better if you can post the entire configuration of your pc-it will enable us to make proper recommendations after taking your needs into consideration.
thaks for advise.... and my pc config is written below
intel core 2 dou
320Gb hdd
250watt psu
intel G31/33 motherdoard and the worst part is that its a slim cabinet
if i miss something then remind me but i think that is enough to know
