When i start my dell insipron N5010 i get 7 beep sound with no display.After s doing some tips and trick i was able to start thescreen. But meanwhile after logginto my desktop all of a sudden it crashes with the blue error screen. and then again it starts beeping without any display. Please help me out!

SOURCE: dell power edge 2850 make 4 seconds beeps alarm

I don't understand the beep code you describe, but the 2850 has many beep codes to help understand what is going on.

First ... Identify the beep. Does the beep start as soon as you power it on, or after several seconds? What is the pattern of the beep - is it a repeating set of beeps - 3 sets of beeps between 1 and 4 beeps ... like 1 beep-3 beeps-2 beeps, or 3 beeps, 3 beeps, 1 beep? Or is it a steady repeating beep - about once per second?

Second ... is the LCD panel on the server blue or orange? If orange, what is the error code(s) it is scrolling?

If it is a steady, once-per-second beep, it is probably your RAID controller. Does the system boot to Windows/OS ok? If so, use (or install) OpenManage Server Administrator (Managed Node from Dell's Support Site) to check the Hardware Logs and check the RAID array (under Storage/Virtual Disks). If it is not booting to the OS, then go into CTRL-M to see what the status of your array is.