Compaq Presario C300 beeps 4 times

burnt up your motherboard. You will have to replace it

This is exactly the same problem as I have. I have changed the power brick and the battery but the problem still exists. PC World were useless and said it "probably needed a new motherboard" although I doubt this is the issue. It worked when I first put the new battery in, until the initial charge ran out. Did you find a solution?

the flash or blink codes you can log on to this site http://h10025.www1.hp.com/ewfrf/wc/document?lc=en&dlc=en&cc=us&lang=en&product=3213867&docname=c01732674
and reference the blink codes. this is also the c300s service manual so you can go back and forth on other things. but if your swapping the motherboards then my suspect is your power supply. make sure that the C300 is getting 18.5 or slightly above if your on a digital meter. but if its below then it wont have enough power to turn on. speaking of power it could be the jack, the pigtails to the motherboard or a loose connector on the wall male end. so make sure to check your path of power from the wall to the unit. and follow electric guidelines and dont shock yourself. but what I used is a paper clip to put into the male end of the Dc voltand the inside is positive and set your ohm meter to DC 20 and it should read 18.5 v.

check the soluition here
http://www.computerhope.com/beep.htm

Sometimes when a PC gets stuck in hibernation mode, the only way to reset it is to remove the CMOS battery for 10 minutes and replacing it. It resembles a large watch battery and is usually located near the center of the motherboard.

just reinsert your RAM; it will work.

there is a lot of factor for a death pc. ignore it all. just check the following :
1. is the hdd led flashing
2. remove the cpu cab and make sure that the fans are spining for both smps and processor
3. any un usual beeps at startup
4. any onscreen message or a blank screen
5. and bla bla ... ...
so far, let's fix it
1. check power and signal connectors of hdd or replace new .
2. re connect all the power connectors on the mobo or change a new smps
3. de assemble, clean and re assemble all the parts inside if there is any unusual beeps
good luck

Check whether your CPU fan is working. It could be due to Fan malfunction of the cabinet also. Seek technician's help, if not resolved

Compaq Presario C300 support

1. Select model
2. click software and driver downloads
3. select OS
4. audio driver links on top of the table

Sounds like you need a new video cable installed