The frequency settings (refresh rate) on your video card are set to a higher value than your monitor supports. You should be able to boot into Windows safe mode (by pressing F8 just as Windows starts to boot) and fix this.
Otherwise, take it back to your brother's house, hook it up, and change the refresh rate to a lower value (like 70 or 75). Also, make sure you have the screen resolution set to something like 1024x768 just to be safe.
Your brother has a better monitor that can handle that resolution.
Case: Enermax CS-A106USB
P/S: OCZ OCZ700GXSSLI 700W
Motherboard: ASUS P5N32-E SLI
CPU: Intel E6300(idle 35C/load 39C)
RAM: OCZ Platinum Rev 2 DDR2 800 MHz (4 x 1GB) 4-4-4-15-T1 (2.1v)
Hard Disk: Seagate 2x250GB SATA ST3250620AS in RAID1
Monitor: Mitsubishi DP900u
Graphics: BFG GeForce 8800GT PCI-E
Sound: SoundBlaster X-Fi Fatal1ty
Speakers: Klipsch ProMedia v.2-400 4.1 speakers
Optical: LiteOn 16X DVD-ROM; Sony DRU-710A DVD-RW