Upgrading pc main parts?

[Regulaser]

Last year I bought the Asus cg5270 assuming that eventually I could put in a new psu and graphics card and be good to go. Now I realize that was a mistake. So here's what I want to do -

Replace the main components of the computer (motherboard, ram, psu, video card, and CPU) with these parts

Motherboard: (not 100% sure, advice would be nice)
Psu: corsair 850w
Video: gtx 570 or 580
CPU: i5 2500k

What I'm wondering is can I do just that? Will it be possible to buy those parts, keep my current case, dvd, and hd(reformat if needed) and be all set? I know it might sound strange but is this a smart idea or should I just build an entire new system?

 

[Sky03]

I'd say dvd and hdd yes. The others you're better off buying new.

 

[Regulaser]

I'd say dvd and hdd yes. The others you're better off buying new.

Would I be able to keep my hdd as is or would I have to format it? Obviously if I didn't have to format that would be awesome.

 

[Sky03]

Would I be able to keep my hdd as is or would I have to format it? Obviously if I didn't have to format that would be awesome.

Sorry i've never used an hdd from a previous system onto a new one so i'm not sure. If i were to guess, i'd say yes you have to reformat.