What is wrong with my laptop!? (beachballing)

[Niteace]

Hey all, any help with this would be great!
I've tried everything i know of with no luck.

I have a mid 2009 MacBook pro.

It started beach balling frequently(for apparently no reason),

to the point it would become unresponsive and I would have to hold the power button for 5 seconds to restart. I had a smart status monitor installed which kept throwing I/O errors for the hard drive. So naturally I assumed it was the drive failing. Then the mac started showing a folder with a question mark at boot and wouldn't load. So I attempted to reinstall snow leopard. After the 3rd attempt it eventually worked. But the same problems persisted. So I replaced the drive. The computer worked perfectly for 2 days then the same issues have cropped up again, to the point it's unusable now because of all the crashing. It also keeps saying the login keychain is missing! Which it did with the old drive too.

I have ran the hardware testing utility on the original install cd which showed no errors n the hardware.
I have also reset the pram (holding alt control p&r at boot) and run repair disk permissions numerous times on the old drive and new)

So I'm stumped !

Any insights?

 

[Ccrew]

Bad memory? I'd have suspected HDD first also, was the switched in one new/known good?

Did you do a restore from a possibly corrupted backup?

 

[Niteace]

I did a restore onto an external drive, same issues. Then I bought a brand new internal Sandisk ssd and a clean install. Again same issues. Although I did copy over my files, unless a corrupt file is causing the issues? I also downloaded a program to test the memory with no probs.

 

[Niteace]

Could it be the logic board? (I'm hoping not, but does anyone have experience of this?)

 

[sjinsjca]

Have you checked for a malware issue? Flashback was in the news recently... see http://unvexed.blogspot.com/2012/04/check-and-protect-your-mac-or-linux.html