Do I need to upgrade my PSU?

I currently have a 450W Rosewill Power Supply that came with my case, with two 12v rails each with 20 amps. My initial build was using an Athlon 64 3200+, 1gb of RAM, and a Geforce 7600GS. Now I've upgraded to 2gb of RAM and an AMD Opteron 170. I've been having some horrible issues of crashing every couple of hours ever since I upgraded last week. Is the new Opteron sucking up too much power?

Would it be better to just get a new PSU, or get some thermal paste and go back to my Athlon 64? Or maybe my Motherboard got hosed in some way, so I'm thinking my best bet is to get a new CPU, Mobo, and RAM (and reuse the old GPU). I have picked out a Core 2 E4300, I believe that uses about the same amount of power as my old Athlon, so hopefully it works.

And as for Newegg's 7 day policy for refunds on CPUs, it mentions 7 days after the date of invoice, what does it mean by that? Because I'm hoping to get a refund on my CPU and Memory to help pay for this new system. I ordered it last Monday, so hopefully tomorrow it lets me file a refund.