how much is this worth?

I would like to sell this custom built computer i have but im not sure how much it is worth any advise?

Black Case, Silver Front with Mac Logo (sorry i didn't make it)

Corsair HX620W Modular Power Supply

Motherboard
CPU Type 2x , 2400 MHz quad core q6600
Motherboard Name Asus P5KC
Motherboard Chipset Unknown
System Memory 4096 MB
BIOS Type Unknown
Communication Port Communications Port (COM1)
Communication Port RIM Virtual Serial Port v2 (COM7)
Communication Port RIM Virtual Serial Port v2 (COM8)

Display
Video Adapter ATI Radeon HD 4800 Series
Video Adapter ATI Radeon HD 4800 Series
XFX Radeon Hd 4890 1GB VRAM GDDR5
2Front USB's
4 Back USB's
PS/2 Connections
Broadcom 802.11g Network Adapter

Multimedia
Audio Adapter High Definition Audio Controller [NoDB]
Audio Adapter High Definition Audio Controller [NoDB]

Storage
IDE Controller Standard Dual Channel PCI IDE Controller
IDE Controller Standard Dual Channel PCI IDE Controller
IDE Controller Standard Dual Channel PCI IDE Controller
SCSI/RAID Controller AA6H3LZE IDE Controller
Floppy Drive Floppy disk drive
Disk Drive ST3750640AS ATA Device (698 GB, IDE)
Optical Drive GLYJ QRST2Z45QR8 SCSI CdRom Device
Optical Drive GLYJ QRST2Z45QR8 SCSI CdRom Device
Optical Drive SONY DVD RW DRU-190S ATA Device

No Monitor or Installed OS

Network
Network Adapter Atheros L1 Gigabit Ethernet 10/100/1000Base-T Controller
Network Adapter Broadcom 802.11g Network Adapter

If someone was to reply ASAP i would really appriciate it, thanks.

To be honest, I think you'll be looking at around £200 - £250. It might be better to split the PC up, sell the PSU, RAM, Motherboard, Graphics Card individually as you may be able to get a little more for them doing it that way.