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I recently installed a dual boot with my windows 7 to try it out. After checking it out i shut it down so i could use windows for school. Now my pc won't turn on at all. Can't even get into bios. After hitting power its black and flicks off after like 7 seconds. I need to use windows!!! I installed both on c drive and didn't set a default. Not even ubuntu starts so now my laptops useless. Im on my phone now. Please help.

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I only have my laptop and phone now. I need booting keys. I tried del f2 f8 etc – Kyle May 23 '12 at 17:46
Do you see only black screen? Or there are any bios messages / welcome screens, etc? – Andrejs Cainikovs May 23 '12 at 17:50
Only black. Its almost like he mobo won't start. I should also note that when shutting ubuntu down it closed down in like 5 seconds had a black screen with some white typing then d had a flicker. Idk if that's normal for this os. – Kyle May 23 '12 at 17:54
Sounds like it's a hardware problem, rather anything related to software. Try to unplug power adapter and remove laptop battery, connect it back after couple of seconds, and try to boot, and come back it worked or not. – Andrejs Cainikovs May 23 '12 at 17:56
Ok did a battery disconnect and now i can get to the boot menu. Im running windows now. Was that a freak accident or is there a problem having both os on one hard drive? – Kyle May 23 '12 at 18:15

Sounds like it's a hardware problem, rather anything related to software. Try to unplug power adapter and remove laptop battery, connect it back after couple of seconds, and try to boot.

There are some machines on which Linux will freeze, after a restart or a shutdown command is issued, right at the very end of the process forcing you to do a hard reset – press the reset/power button the system or plug the cord which is not good. In this post we will see how you can resolve almost 99% of freeze/hang that occurs during shutdown or reboot.

Why this happens

There are many reasons why this happens – some times it is an BIOS issue or sometimes it’s just that your system has a different kind of hardware setup, for example no keyboard controller, and Linux (the kernel) does not understand how to tackle that situation. Most of the time if it is a BIOS issue it is not very easy to ask your system vendor to give you an immediate BIOS fix that will take care of the issue and hence you have to rely on some kernel parameters that you need to pass to fix the hang/freeze issue.

Let’s say you bought a new machine and you notice that your Linux distribution hangs at the very end of the reboot/shutdown process, upon giving any of the following commands:

# shutdown -r now
# shutdown -h now
# reboot
# halt
# poweroff
# Ctrl+Alt+Del


In order to fix the issue, you should try one-by-one passing the following parameter to the kernel, in the form of reboot=<parameter>, at the time of boot:

warm =  Don’t set the cold reboot flag
cold = Set the cold reboot flag
bios = Reboot by jumping through the BIOS (only for X86_32)*
smp = Reboot by executing reset on BSP or other CPU (only for X86_32)
triple = Force a triple fault (init)
kbd = Use the keyboard controller. cold reset (default)
acpi = Use the RESET_REG in the FADT*
efi = Use efi reset_system runtime service
pci = Use the so-called “PCI reset register”, CF9
force = Avoid anything that could hang.

As per my experience, one of the parameters (with the asterisk above) should be able to resolve your hang (or freeze) issue 90% of the time: reboot=bios or reboot=acpi.

Once your system boots you can verify whether the parameter was correctly passed or not by issuing the following command:

cat /proc/cmdline


root=/dev/sda ro vga=791 quiet reboot=bios

You can find the list of all the above parameters in the reboot.c file in the Linux kernel source.

By default, the Linux kernel uses the reboot=kbd method i.e. it tries to look for a keyboard controller and issue a reset/shutdown command to it. But there are some systems like some of the Intel Atom processor based machines that don’t have a keyboard controller and the above fixes are required. If you read the reboot.c file carefully there are some major main stream machines from Dell, Sony, HP, etc. that require the above “reboot=” fix. I guess sometime it is easier to fix the issue by using the kernel parameter rather than fixing in the BIOS.

Also you can also use the first letter (as denoted in the “[]” brackets) of each of the parameter:

reboot=b        # for reboot=[b]ios
reboot=a        # for reboot=[a]cpi

and you can pass multiple parameter at the same time and Linux kernel will try in order specified:

reboot=a,b,k,c  # for reboot=acpi,bios,kbd,cold

Credit goes to Kushal Koolwal.

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