That's probably your problem. I had a similar case where my PS2 worked for awhile after I got it modded, but after it stopped working and led me to the RSOD. I got it fixed later and found that it was either a wire loose or a bad modchip. The installer changed the modchip and now it works perfectly!
Don't give up hope! It's probably a wire or the chip! (Most likely the wire coming off!) Have Fun! and Good Luck!