Computer cannot boot - just beeps when switched on

A one second beep from the computer is standard for a proper boot.
Do you have a TV that you can plug your computer into to see if it is posting video? That would be the easiest way to test if it is a computer or monitor thing.

The long buzzing sound indicate the nature of the problem. Depending on the manufacture of your bios will determine the problem. With only one long beep you may have memory problem. The computer cannot initiate the boot sequence. Did you add any devices to the computer prior to your problem. if you did undo what you did. Make sure the computer is on, if nothing happens ( no lights, no sound, no fans etc.) the computer has a power failure. Make sure you listen to the beep if it is a numerous beep sequence note it down and check the web for computer beep during boot up.

The motherboard is not telling you there is no signal, the monitor is..
In this order:

1. Test the connection from graphics card to monitor, try a different monitor to eliminate this from the issues.
2. If other monitor works, the old one is causing the problems
3. If new monitor does not work:

• Check the graphics card is seated properly, if possible, test with another graphics card, if this works, the issue is with the graphics card
• If this does not work, check the fan on the cpu, is it spinning? If not, make sure the fan is connected to the motherboard
• If the fan is spinning, remove all the ram, reboot, you should get a series of beeps, make note of these and repost them (computer will not boot)
  
• If you get NO beeps with ram removed, the CPU or motherboard are possibly dead, if possible, replace CPU with known working one and retest with and without ram in, make sure you have thermal grease on the CPU>heatsink. Replace the Ram (or one module)
  
• If you get a single beep and the motherboard powers the monitor, the CPU was your issue
• If you get no beeps, confirmed death of motherboard.

Possible other solutions: Remove CMOS battery, leave for 1 minute and then replace, see if it boots
Check the power switch from the computer front panel is not sticking

If you hear exactly ONE beep, it means that your computer-hardware (power-supply, CPU, motherboard) is OK.
Multiple beeps are "bad" -- they identify different errors.

If Windows does not "boot", then the power-surge may have damaged your 'C:' drive. Ouch!

Yes if there are error on the system you should most likely hear a beep most of the time when there is no beep it is due to bad ram. Some times beep codes can't detect bad ram and your computer will not boot.
Open the computer up and see how many ram chips you have if you have more than one take the one in dimm slot 2 out. There should be small writing next to the slots 1,2,3,4 or Dim 1 dim 2 ect ect. you always want to keep slot 1 with ram so start by pulling out the ram out of slot 2 and turn your computer on. If your computer still dosn't post pull the ram out of slot 1 out and insert the ram that was in slot 2 into slot 1 if still no luck it's most likely your board but the best way to test this is to know that you have a good working stick of ram you could purchase one and if it dosnt work bring it back ... theres also the chance of your video card being bad but there is usualy a post code for it (beep code)
if you have no clue on what ram looks or how to open your computer just google for installing ram on a computer and you should find step by step guides

Does the computer Beep at all. If it does, and it beeps differently now than it did previously then that is a POST code and indicates a serious problem. If it Beeps like it used to but there's no video then you should still hear the hard disk clicking - that would be a Video card problem (or perhaps the monitor). If it doesn't Beep at all and it does not make a clicking noise then your BIOS, or Motherboard may be damaged.... perhaps by a failed, or faileing power supply (?)

Please check your plug if it is plug in properly or firmly. Locate the switch and turn it on again. If stil persist, try to inspect whether cpu is beeping while turning on. If its beeping something is wrong in your cpu or monitor depending upon the beeps.

do you see the light blinking in the monitor? I mean the POWER led light up? If so, then the monitor is ok and is working good. It is your CPU which has a problem and not sending digital signal for the monitor to display.
Try to turn off your computer. After 3 minutes turn it back on. then notice if you will hear a short beep from the CPU. That signals a successful video initialization. If you went through that process, then your computer will get back to life.
However, if you dont hear a short beep from the CPU, then definitely your CPU is frozen therefore there is nothing to display to the monitor.
You need to open the CPU case, pull out memory modules then plug them back in. Then try booting.
If not successful, try to open case and pull out the processor. Put it back in after 30 seconds. Try booting again.
Do ALL THESE while your PC is UNPLUGGED.
Good luck.

Have you check the video card, is it loose, not sitting right, beeps are either memory, video or a bad mobo. here's a list of beep codes; the numbers represent the amount of beeps
1   The memory refresh circuitry has failed 2   Parity errors have been detected in the first 64 KB of memory 3   A failure has occurred within the first 64 KB or memory 4   System Timer failure: Timer 1 on the mainboard does not work properly 5   The CPU has generated an undetectable error 6 8042 Gate-A20 failure: BIOS cannot switch the CPU into protected mode 7   The CPU has generated an exception error 8   The video adapter is missing, or the memory on the adapter has generated a failure 9   The ROM checksum value does not match the value in BIOS 10     The shutdown register for CMOS interrupt channel 2 has failed POST; the system board cannot retrieve CMOS contents during POST 11 Level-2 cache memory has failed the tests, and has been disabled 2 short POST has failed, caused by a failure of one of the hardware tests 1 long, 2 short Failure in video system: a checksum error was encountered in video BIOS ROM, or a horizontal retrace failure has been encountered 1 long, 3 short Failure in video system: the video DAC, the monitor detection procedure or the video RAM has failed 1 long POST procedures have passed

is there a post beep when the pc is switched on. check the memory if it is a beep beep beep sound , also disconect the hard drive, dvd drive, floppy, and any usb devices and see if it boots up. if that fails it does seem like the mother board, also check the cpu fan has it stoped. also find out the power switch conector on the mother board, from the base unit switch to the mother board. also chech the power connector from the power supply to the mother board , on newer boards there are two that go to the mother board its self , a big one and a very small one .