powercolor ATI Radeon HD 4850 will not overclock?

. 1 Intel Core 2 Duo E7400 Wolfdale 2.8GHz LGA 775 65W Dual-Core Processor Model BX80571E7400
. 1 G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Dual Channel Kit Desktop Memory Model F2-8500CL5D-4GBPK

. 1 Western Digital Caviar SE WD3200AAJS 320GB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drive -
. 1 POWERCOLOR AX4850 512MD3-DH Radeon HD 4850 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card -
. 1 GIGABYTE GA-EP45-UD3L LGA 775 Intel P45 ATX Intel Motherboard
. 1 RAIDMAX SMILODON Extreme Black ATX-612WEBP 1.0mm SECC Steel ATX Mid Tower Foldout MB Computer Case With 500W Power Supply - Retail