CPU heating up way too much

[JefeRafa]

Hey guys, really new here and signed up because I really need a bit of help on this! I'm currently working on a small project and doing a scrapyard wars thingy with some friends. We live in a country where pc tech is kinda behind with the rest of the world, so lets just say I got really lucky getting my parts for a cheap build (Which seems i'll have to use as my main pc since my own build died but that's another story). The sad part is that the cpu is heating waaaaay too much and i've tried everything! Replacing heatsink on fans, new thermal paste, more fans on the case, staying in a cold room... I keep getting temps on 80-90ºc idle! I've tested the cpu on other boards and it's not giving me that issue at all. I'm stuck with stock fans because in my country, lga775 aftermarket fans are impossible to get.
Core 2 Quad Q8300  @ 2.50 GHz
ASrock G31M-VS2 Motherboard
DDR2 4gb @ 332.4 MHz
Nvidia gtx 750ti
ITEK 550w power supply.

Honestly I got my giblets in a vice here because all I have to replace it is a Dual-Core E5400, which might just make me lose this one (I'm kinda new into this whole thing, so i'll assume it's a worse cpu). Please help! And thank you.
 

[i3iorn]

Are you testing in open air or in a case? Did you test the other boards in the same conditions? Have you checken that the cpu actually runs a 2.5ghz or are you going of the specs?