Troubleshooting probelms/Upgrade components

Built a little over 5 years ago

AMD athlon 2.0Ghz

Asus m2n-sli

seagate 250gb 7200

earthwatts 500w green

antec nine hundred case

some cheap a$$ XFX card that was in stock at best buy when my Geforce 8500 kaputt

Problem: I can hear my hdd engage and disengage 10-12 times before passing post, probably a over 30 sec duration

I have had issues with this hdd before so I Replaced hdd with seagate 500gb 7200 best buy had in stock, new cables. Same issue. Unplugged cd drive and all my fans to take load off of PSU. Same problem. Replaced PSU with a new earthwatts 500w green cuz of $40 off sale. Same issue.

Do you guys have any suggestions on where to look next?

I'm guessing my mobo is bad... if so what would an upgrade recomendation be? I supposed I'd like to upgrade my mobo, processor and ram for around $200

I'm a low maintenance gamer, mainly just word processing and internet. Games I played are usually on low settings like Battlefield 1942, CoD World at War, and now World of Tanks/Warplanes...you know. WW2 stuff

I appreciate any advice!

Btw, it all started out of the blue about a month ago... Also, if I tried to put it on stand by mode the whole computer would restart. Was running XP pro, bumped up to Win 7 with new hard drive

if you only play old low end games the new Trinity will be fine 

http://www.newegg.com/Product/Product.aspx?Item=N82E16820231468

http://www.newegg.com/Product/ComboDealDetails.aspx?ItemList=Combo.1076923

about to $240  just add a new videocard over next 5 years and your good go.

intel build 

http://www.newegg.com/Product/Product.aspx?Item=N82E16820231428

http://www.newegg.com/Product/Product.aspx?Item=N82E16813157303

http://www.newegg.com/Product/Product.aspx?Item=N82E16819116777

for $225

Thanks for the suggestions. I'll check them out... based on my symptoms, does that sound like replacing the motherboard is my problem fix?

It couldn't be some fault in the start button on my case or something screwy like that? I know just replacing stuff isn't the correct way to troubleshoot computer issues, but I figured 5 years was enough wear on some of those parts