Acer Aspire Predator 2008 model
Ram:8gb (was 4GB, but recently added 2x2gb 240pin DDR2 from crucial)
OS: Windows vista 64bit
Processor: AMD Phenom 9750 quad core 2.4ghz
Graphics: Radeon HD 4850 1GB
power supply: 500/750W (unsure which)
Motherboard: Unsure
Monitor: HP w2408h 24"
keyboard: razer Arktosa
Mouse : R.A.T 7
I took off my Pc case today to air dust the computer. I didn't touch anything inside the case and used anti static wristband while doing this. When i replaced the side panel and booted up the pc, it worked fine until reaching the windows vista login screen where the monitor what was working previously, kept going to sleep by itself and wouldn't display the logon screen.

Me and my brother held down the power button for 5seconds to turn it off (as we couldn't see the screen), removed the side panel and made sure all the connections were where they should be.

After checking, we replaced the side panel again and the same thing happened. We also tried my brother's monitor which also acted the same way. We then turn it off again, and ran it in safe mode, which worked perfectly (for safe mode). We turned it off, tried it in normal mode, which had the same problem as before.

The computer was working fine before I air dusted the inside.

So, me and my brother have hit a brick wall and do not know what to do next, or what to try, and any advice would be welcome.