Should i use this old coolermaster psu?

Solution
It would probably be a good idea to replace it if you can. That's already a lower quality unit and power supplies degrade slowly over time. Rather than chance any issues, a new one would be preferable. Some psu's can fail and it only means your pc loses power, others depending how they fail can take other components down with them. Even if the chances aren't 95% of that happening, it's down to whether you think it's worth risking it at all.
It would probably be a good idea to replace it if you can. That's already a lower quality unit and power supplies degrade slowly over time. Rather than chance any issues, a new one would be preferable. Some psu's can fail and it only means your pc loses power, others depending how they fail can take other components down with them. Even if the chances aren't 95% of that happening, it's down to whether you think it's worth risking it at all.
 
Solution
As synphul said, it's a good idea to keep it, however it might run for 5 years more, no guarantee, to this day I don't know the brand of my psu and it has held a gt 8600, gts 250 and now a gtx 650 and it just doesn't want to die, so if budget is a trouble you can run with it.
 


Hi - Ti piggyback on the prevailing opinion, this is from "johnnylucky" .org Lemon List:

"GX-650 650 Failed efficiency rating. Failed load testing. Medicore voltage regulation. Poor DC output quality on 3.3V rails. Outdated design". Hard OCP
http://www.hardocp.com/article/2010/11/22/cooler_master_gx_650w_power_supply_review/