Had problems myself with my slim. I fixed it by using the stock 3.41 file to go from 3.50 to 3.41. Give that a shot and see if it helps. It should do the trick if your are on 3.42 or 3.50 as there is no downgrade for 3.55 yet and you didn't mention your current firmware.
PS3 CECH-2501A [CFW] & CECH-3001 [OFW]/ PS2 SCPH-3901 & SCPH-7501/ PS1 SCPH-5501
Mod Cobra 4.46 v7.00 w/ E3 Flasher [CFW] & Cobra ODE 4.50 [OFW]/ Mod HDD-OSD [Phat] & Modbo 4.0 [Slim]/ Mod MM3
HDD 1tb [CFW] & 640gb [OFW]/ HDD 640gb & OPL v0.92 w/ 1.5tb SMB