PC boots, but CPU fan just twitches

First off, here are the parts I got for my PC.

Mobo + Optical Drive: Biostar A785G3 + Sony Optiarc CD/DVD Burner Black SATA Model AD-7260S-0B - OEM

CPU: AMD Athlon II X3 440 3.0Ghz AM3 OEM CPU


GPU: XFX ATI Radeon HD 5770 1 GB DDR5

RAM: G.SKILL 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10600)

HDD: Western Digital Caviar Blue WD5000AAJS 500GB

PSU: Antec EarthWatts Green EA-380D Green 380W

Case: Rosewill R102-P-BK 120mm Fan MicroATX Mid Tower Computer Case

Front Case Fan: Bgears B-Ice Silver 120mm Blue LED Case Fan

Last night I put my first desktop together using those parts. Everything fit well so I wired everything up and turned it on. Unfortunately the CPU fan does not turn on, but instead just makes a little twitch every couple of seconds or so, so I then turned it off. I checked the connection for the CPU fan to the motherboard and it is connected well. My other fans turned on though, the motherboard would beep and it doesn't seem to be beeping a pattern that says there is an error.

I then tried to connecting it with a monitor to see what would happen. I turned on the PC again with it connected to the monitor and it would go all the way where it would be waiting for something to boot from. This also shows the status of the hardware and under CPU fan RPM it would say N/A. At first the CPU's temp was 34 C, but I let it run for a few minutes then restarted it again and this time its temp was 70 C.

I guess at this point I'm thinking there is either something wrong with the CPU fan and heatsink or something wrong with the CPU fan connection on the Mobo. I guess the next move would be to try the CPU fan under the sys fan connection on the mobo and try one of the case fans attached to the CPU fan connection. I guess I want to know is that those suspicions going in the right direction, or is there something else that im missing?
11 answers Last reply
More about boots twitches
  1. Hi, make sure nothing is being shorted inside your case, it is very easy to happen and very frustrating to diagnose. Check if the stand offs are installed properly, check if the CPU paste is not shorting the motherboard, check if the CPU itself is seated properly, there are many things that can go wrong. post some pics if you can.......dude i just noticed you are using a 380W powersupply?........I think you might run into problems later on with that Wattage.....i Would say go for 550W...heat can effect the efficiency of your PSU exponentially. GL dude.
  2. The case doesn't use standoffs, but I guess thats what I get for using such a cheap case. It just has bumps for where the standoffs would go, and since it makes it the mobo fit I guess it's seated properly.

    CPU is definitely installed correctly, since I checked that a few times before I put the heatsink in. Maybe I should check the TIM (used Artic Silver 5) since when I put the Heatsink on I wasn't able to keep it flat on the CPU the entire time (it required alot more force than what I expected).

    Im not too worried about the PSU since both the CPU and GPU are very energy efficient. Heck it was pretty much recommened here at Tom's at their last $550 budget gamer's build earlier in June.

    Can't post pics now. Got to get going to work :(
  3. I wanted to add something to this that may help you... with that said i am by no means an expert.

    I recently had a similar problem with a build. The system would not completely boot and it gave an fan error message.

    I had the fan plugged into the MOBO in an incorrect slot (the CPU fan for that particular mobo had to be plugged into a specific slot)

    just as a suggestion try to confirm that the fan should not be plugged into another slot.

    hope this helps with your problem.
  4. Well try running your computer without the graphics card, 1 stick of RAM, and only 1 drive.
    If it works after that, your 350w PSU is probably not enough OR one of the parts you just took out.
    Also, after you have started your computer with the bare minimum, start installing things one at a time until you figure out what caused the problem. If the problem happens after a random component is put on, the it's probably your PSU. BUT if it happens only when a certain component is plugged in, try replacing that specific component.
  5. Also, I doubt the built in stand-offs in your case are the problem UNLESS one of them is touching the board where there is no hole...I myself use a cheap case too :)
  6. after a second look, if you have not used standoffs that may be your problem. after a quick search it seems that more than a few people have recieved this case with either not enough standoffs or none.
  7. archer7282 said:
    after a second look, if you have not used standoffs that may be your problem. after a quick search it seems that more than a few people have recieved this case with either not enough standoffs or none.

    Archer may be right! I read the review about the complaining customer. It's true that some cases come with SOME built-in stand offs but they still require one or two to be manually put in. At least mine did.
  8. The case only came with one standoff, and I don't really know where to put it. I have tried running it with memory, GPU, HDD and optical drive, and cpu fan still doesn't start up. Tried connecting one of my case fans to the CPU fan connector and it works there, but then I tried connecting the CPU fan directly to the PSU using an adaptor and it still doesn't work. Is it wrong of me to think that I probably need to replace the CPU fan?
  9. To check whether you have enough standoff and whether or not they're in the right place, put a piece of cardboard over each stand off and, with a marker, mark each of the standoffs. After that, place the piece of cardboard under your mother board and make sure that the number of holes is equivalent to the number of standoffs. IF there are fewer standoffs then there are holes then you might want to figure out which standoff is missing and then add it.

    If you connected another fan into the CPU fan connector and it worked, then chances are that your CPU fan is not working.
    You can probably just replace it, or if it's attached to the heatsink and it can't be moved then you might have to change the entire heatsink.
  10. Just as a thought, maybe what you're experiencing is normal? A while ago, I built my HTPC (Intel Core2Duo E6600) and noted the same thing as the OP. The CPU Fan would just twitch when the system was first powered on. After about a minute, it would start to spin normally. This system has been running 24/7 for the last couple of years; up until a few days ago when I decided to rebuild it. Putting it back together, I again noted the CPU Fan "twitching" (this is why I remember). I've never gotten any type of CPU errors and the CPU Heat sensor my case has usually sits around 40c.

    -Wolf sends
  11. Interesting.
    I've never heard of a twitching cpu fan being normal, but hey! if it works for you Wolfshadw, why question it? lol

    If you do decide to let it be, Jerico, I would constantly monitor my CPU temperature just to make sure. Do you have "Quiet n' Cool" or something like that in your BIOS? I don't remember the exact name but I have it in mine and sometimes the fan speeds drop a lot. Although, it never just twitches. :) You could try disabling said option in your BIOS.
Ask a new question

Read More

Homebuilt CPUs Systems Product