Spontaneous reboot

The day after reinstallation of Win98SE (on 2.2 Gb
Pentium 4 with 512 Mb RAM) there was a spontaneous
reboot while connected on line (phone line) with running:
Internet Explorer v.6
RealPlay
Magix Audio Cleaner (recording software)

I fear possible hardware problems in this PC (new in June)
e.g. (1) after rebooting with a disk in drive Q: (master 2)
Win98 does not detect drive H: (slave 2)
(2) Anomalies in power supply which (once a week)
requires me to switch off at back panel and on again
before the front panel On/Off switch works normally.
(3) I earlier downloaded Windows Media Player 9.
After reinstallation of the OS WMP plays MP3s at double speed.

I could not find anything appropriate in the MS KB.
Advice?

--
Don Phillipson
Carlsbad Springs
(Ottawa, Canada)