I have a Dell vostro 420, which was bought two years ago.

Today, I can not start the desktop.

After I pressed the start bottom, the power light on, the hard drive light was on once then off, all the three fans, the cpu fan, the case fan and the video card fan are working, but no beep alarm, no outpout signal to my monitor.

I tried to open the case, it is pretty dusty inside.  I unplug the video card and cleaned it.  I unplugged the two memories and cleaned them.  I put the video card back to the slot, leave the memories slot blank and then restarted the computer.  Now the computer began to beep, showing the memories are not ready.  After I plug the memories back, the same thing happened again:  no starup alarm, no signal output.

I used the computer last night, it was working ok but I noticed that there are some abnormal color flakes on the monitor, though not very apparent.

I found that office depot and staple can fix the desktop for 300$ bucks, it is too much for this old computer.  Can anyone help me with this?  Thanks a lot!

Configration: 

cpu 7400 dual core.

2x1 2G 6400 memory

250G hd

HD4850 HIS video card