hay... 1st post...
so wellcome to the forum....
hmm... may be a virus... so.. have u scaned the system with any GOOD avs like NAV or KAV??
2nd thing... but confusing... as u said that "clearing offline contents" templly solves ur problem...
as if that wouldnt happend... i would have written that may be a problem either with system power supply or with the MOBO....
so 1st thing 1st... make sure u have scaned the system with good antivirus... & u have the latest driver for ur modem... considering loading the SP2... & if internel modem then try to switch the PCI slot... or if Serial modem then try to switch the port...