probably itz either
minor case of software corruption/improper ground/cpu fan..or
major case of faulty or defective main board/ram/daughter or addon card(s)..
..plz do check the following as in order:..the Hardware part
1)a)in power on mode, open/unplug the data/vga cable of the monitor fromcabinet..see if raster or 'osd' is appearing on the monitor screen..ifso monitor is ok..else replace the monitor and see..[not applicable in case of laptop]..b) in case of laptop try to get output from external display unit/monitor using vga port..if there's proper display in there..the problem is probably with either the 'lcd' or 'ccfl' or 'inverter circuit'..
2) if u hv a graphics card, replace with a standby or onboard and see..[not applicable in case of laptop]..
3) unplug mains supply..pick open/remove the cmos battery..check (above +3v)..resit..
4)seeif the ram(s) is loose/faulty..open clean/remove carbon & or oxideformed on the teeth with an eraser n resit it..or replace with a standbyn see..
5) a) see if ur hdd is noisy or emitting any 'ticking'noise (like 'tuk tuk' or 'kirr kirr')..
b) or if the system is not supporting either the newly installed device or itz software/driver /firmware
if so, u need either a fresh os installation or ur hdd is likely to breplaced..
6)remove/clean dust neatly..dust is non-uniform innature n may cause jam/short circuitry/excess resistance n manymore..resulting an increase in heat..
7) open the CPU Heat-Sinkwith fan out of the socket..put some "Heat Sink Compound" (available inlocal electronics chip level spare market) between the cpu/processor andthe CPU Heat Sink *** fan..resit/fit it tightly in position..
8)on main/mother board..see with a debug card for mb error..may bshort..look for defective capacitors(esp above1000mfd)/mosfets..gothrough the mb's south bridge n the circuit lie around atxconnector..the crystal clock generator (if cpu isn't heating up)..
9) [in case of desktop] the smps itself may b defective/faulty..check the outputs of smpsviz. 0v (black~ground); +12v (yellow); +5v (red, green~ps-on, violet~pg& grey~sb); -12v (blue); -5v(white); +3.3v(orange)..the 'oscillator and error amplifier ic', orpwm switching regulator circuit..look for defectiveprotector-transformer/resistance(esp 4.7k)/mosfet..check the battery n adapter [main power], in case of laptops..the Software part:..
1)hv a licensed and UPDATED antivirus installed (iprefer avg/kaspersky, remember, without updation a full version antivirusis useless)..
2) download, install n run microsoft kb890830..http://www.microsoft.com/downloads/details.aspx?FamilyId=AD724AE0-E72D-4F54-9AB3-75B8EB148356&displaylang=en
3) download n run Startup Control Panel..http://download.cnet.com/Startup-Control-Panel/3000-2094_4-10039330.html
..'removeall the unnecessary startup items from here..(if u can't find whatto remove, post me/us in ur comment with all the items listed in eachn every tabs herein)..
4) remove all unnecessary software from add/remove programs..
5) download, install n run 'Advanced System Care Pro'..http://download.cnet.com/Advanced-SystemCare-Pro/3000-2086_4-10399324.html
6)disable the following:..
a)'Automatically Restart' right click on mycomputer->properties->advanced->startup n recovery->(uncheckon the) Automatically Restart;
b)'Error Reporting' right click onmy computer->properties->advanced->error reporting->disableerror reporting->(uncheck on the) 'but notify me when criticalerror occur'..
7) Increase the size of Virtual Memory, Initial: 1440; Maximum: 2880
if u r bot a professional, always better to seek advise from ur system admin/vendor....