6 beeps at start up - Gateway Essential 400 PC Desktop

parking sensor beep?
if yes then if one of the sensor fails then all system goes off and keeps buzzing

if it is a continuos repeated beep beep sound your hdd cable is loose and if it comes at boot time only it is the sound for ram testing which says ram isok
if a continuos long sound comes and pc doesnot start it is the case of ram fault try cleaning contacts of ram and ram slot with alcohol methyl or spirit or Absolute vodka works best.

Beeps always indicate error excluding a one single beep only which indicate process.Every manufacturer has its own beep setting. it comprises on short and long beeps. If previously it working good, then your idea may be correct. replace both the keyboard and mouse with existing. start computer if now it not giving beeps it meant that one of them is causing problem. connect one by one and start computer you will reach. AND if even after replacing keyboard and mouse it gave beeps then shut down your system. Open casing remove processor and memory chip out and connect them again it will work now INSHALLAH.

there are 4 kinds of beeps that the pc produce when you turn it on, base on your beep it is indicating that the memmory is damage,

a single beep means the pc is ok
and your beep is memmory damage
a long beep pause and then beep long again means video card damage
if the beep sound like a firetruck the processor or memmory is over heating

Temporary Fix: unplug the dryer or cut its power at the circuit breaker panel, when not in use. If the dryer alerts/alarms are set to silent and the beeping happens when it's not in use, chances are it's the same beeping you hear when you first introduce power to the unit or press start. This may indicate a short affecting the control board. If you need to press start multiple times to get the dryer started, then the control board components are most likely starting to fail.

http://www.computerhope.com/beep.htm

listen carefully to the beeps
One Long Beep, One Short Beep= motherboard problems.
One Long Beep, 2 Short Beep= video problems.
One Long Beep, 3 Short Beep= video problems.
Repeated long beeps = memory failure
continious long and short beeps = Cpu overheating

hope this helps

unplug it then plug it back in to see if it helps